Controlling access point transmit power based on received access terminal messages

ABSTRACT

Transmit power for an access point is controlled based on information received by the access point. For example, an access point may employ one or more algorithms that use messages received from nearby access terminals to maintain an acceptable tradeoff between providing an adequate coverage area for access point transmissions and mitigating interference that these transmissions cause at nearby access terminals. Here, the access point may employ a network listen-based algorithm upon initialization of the access terminal to provide preliminary transmit power control until sufficient information is collected for another transmit power control algorithm (e.g., an access terminal assisted algorithm). Also, the access terminal may employ an active access terminal protection scheme to mitigate interference the access point may otherwise cause to a nearby access terminal that is in active communication with another access point.

CLAIM OF PRIORITY

This application claims the benefit of and priority to commonly ownedU.S. Provisional Patent Application No. 61/304,252, filed Feb. 12, 2010,and assigned Attorney Docket No. 101006P1, the disclosure of which ishereby incorporated by reference herein.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to concurrently filed and commonly ownedU.S. patent application Ser. No. ______, entitled “MULTI-STAGE TRANSMITPOWER CONTROL SCHEME FOR ACCESS POINT,” and assigned Attorney Docket No.101006U2, the disclosure of which is hereby incorporated by referenceherein.

BACKGROUND

1. Field

This application relates generally to wireless communication and morespecifically, but not exclusively, to controlling access point transmitpower.

2. Introduction

A wireless communication network may be deployed over a geographicalarea to provide various types of services (e.g., voice, data, multimediaservices, etc.) to users within that geographical area. In a typicalimplementation, macro access points (e.g., each of which providesservice via one or more cells) are distributed throughout a macronetwork to provide wireless connectivity for access terminals (e.g.,cell phones) that are operating within the geographical area served bythe macro network.

As the demand for high-rate and multimedia data services rapidly grows,there lies a challenge to implement efficient and robust communicationsystems with enhanced performance. To supplement conventional networkaccess points (e.g., to provide extended network coverage),small-coverage access points (e.g., low power access points) may bedeployed to provide more robust indoor wireless coverage or othercoverage to access terminals inside homes, enterprise locations (e.g.,offices), or other locations. Such small-coverage access points may bereferred to as, for example, femto cells, femto access points, homeNodeBs, home eNodeBs, or access point base stations. Typically, suchsmall-coverage access points are connected to the Internet and themobile operator's network via a DSL router or a cable modem. Forconvenience, small-coverage access points may be referred to as femtocells or femto access points in the discussion that follows.

When a femto cell is deployed on a carrier frequency that is differentfrom the carrier frequencies used by neighboring macro cells, the femtocell may radiate beacons on the macro cell carrier frequencies. In thisway, the femto cell may attract an access terminal that is in thevicinity of the femto cell to the femto cell coverage (i.e., cause theaccess terminal to move off of the macro cell coverage). Thus, throughthe use of this beacon scheme, a user coming home (e.g., approaching ahome femto cell) from outside the coverage of the femto cell will beable to readily discover the femto cell and obtain service from thefemto cell. Though such beacons are useful in terms of femto celldiscovery, they may create interference on the macro network since thebeacons are transmitted on the same carrier frequency that is used byneighboring macro cells. This interference may affect the voice callquality of active macro cell users (i.e., users actively receivingservice from one or more macro cells on a macro cell frequency) and mayalso lead to call drops if the macro cell user happens to be very closeto the femto cell. Similar macro network interference issues may arisein a co-channel deployment due to femto cell forward link transmissions.Therefore, there is a need to protect active macro cell users frominterference from femto cells while still providing adequate coverage ata femto cell.

SUMMARY

A summary of several sample aspects of the disclosure follows. Thissummary is provided for the convenience of the reader and does notwholly define the breadth of the disclosure. For convenience, the termsome aspects may be used herein to refer to a single aspect or multipleaspects of the disclosure.

The disclosure relates in some aspects to controlling transmit power ofan access point. For example, the disclosed techniques may be employedto control beacon channel transmit power and/or forward link (e.g.,service channel) transmit power of a femto cell. In such a case,transmit power may be controlled on one or more beacon carrierfrequencies (e.g., macro frequencies) and/or on a femto forward link(FL) carrier frequency. Here, controlling the transmit power mayinclude, for example, setting transmit power limits and/or setting atransmit power value.

The disclosure relates in some aspects to multi-stage transmit powercontrol schemes for an access point. For example, a network listen-basedalgorithm may be employed when the access terminal is initialized (e.g.,upon power-up), after which a more robust algorithm (e.g., an accessterminal assisted algorithm) may be employed to provide a bettertradeoff between having an adequate coverage area for the access pointand mitigating interference to nearby access terminals. In addition, anactive access terminal protection scheme may be employed (e.g., on acontinual basis) to mitigate interference the access point may otherwiseinduce at a nearby access terminal that is in active communication withanother access point.

In some aspects, a network listen-based algorithm may involve:maintaining information indicative of a desired coverage range for anaccess point; receiving signals on a carrier frequency, wherein thesignals are received from at least one other access point that transmitson at least one forward link on the carrier frequency; determiningsignal strength information associated with the received signals;setting transmit power limits for a transmit power algorithm based onthe determined signal strength information and the maintained coveragerange information; and controlling transmit power of the access pointaccording to the transmit power algorithm.

In some aspects, an access terminal assisted algorithm may be based onmessages that the access point receives from nearby access terminals.The messages may comprise, for example, measurement reports and/orregistrations messages.

In some aspects, an access terminal assisted algorithm that employsmeasurement report-type messages may involve: transmitting data on aforward link and optionally transmitting beacons on a beacon channel,wherein the forward link data is transmitted on a first carrierfrequency and the beacons are transmitted on a second carrier frequency;receiving messages from at least one access terminal, wherein themessages are indicative of channel quality on the first carrierfrequency and/or the second carrier frequency (and/or wherein themessages include path loss information); and controlling transmit powerof the access point based on the received messages, wherein the transmitpower is controlled for transmissions on the first carrier frequencyand/or the second carrier frequency.

In some aspects, an access terminal assisted algorithm that employsregistration-type messages may involve: transmitting data on a forwardlink and optionally transmitting beacons on a beacon channel, whereinthe forward link data is transmitted on a first carrier frequency andthe beacons are transmitted on a second carrier frequency; receivingregistration messages from at least one access terminal (e.g., apreferred access terminal such as a home access terminal or anon-preferred access terminal such as an access terminal that is notauthorized to access active mode service via the access point), whereinthe registration messages are triggered due to detection of beacons onthe second carrier frequency or detection of signals on the forward linkby the at least one access terminal; and controlling transmit power onthe first carrier frequency and/or the second carrier frequency based onthe received registration messages.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other sample aspects of the disclosure will be described inthe detailed description and the appended claims that follow, and in theaccompanying drawings, wherein:

FIG. 1 is a simplified block diagram of several sample aspects of acommunication system wherein an access point controls its transmit powerbased on received information;

FIGS. 2 and 3 are a flowchart of several sample aspects of operationsthat may be performed in conjunction with controlling transmit power ofan access point;

FIGS. 4 and 5 are a flowchart of several sample aspects of operationsthat may be performed in conjunction with a network listen-basedalgorithm that controls transmit power of an access point;

FIG. 6 is a flowchart of several sample aspects of operations that maybe performed in conjunction with an access terminal message-basedalgorithm that controls transmit power of an access point;

FIG. 7 is a flowchart of several sample aspects of operations that maybe performed in conjunction with a registration message-based algorithmthat controls transmit power of an access point;

FIG. 8 is a simplified block diagram of several sample aspects ofcomponents that may be employed in communication nodes;

FIG. 9 is a simplified diagram of a wireless communication system;

FIG. 10 is a simplified diagram of a wireless communication systemincluding femto nodes;

FIG. 11 is a simplified diagram illustrating coverage areas for wirelesscommunication;

FIG. 12 is a simplified block diagram of several sample aspects ofcommunication components; and

FIGS. 13-17 are simplified block diagrams of several sample aspects ofapparatuses configured to control transmit power as taught herein.

In accordance with common practice the various features illustrated inthe drawings may not be drawn to scale. Accordingly, the dimensions ofthe various features may be arbitrarily expanded or reduced for clarity.In addition, some of the drawings may be simplified for clarity. Thus,the drawings may not depict all of the components of a given apparatus(e.g., device) or method. Finally, like reference numerals may be usedto denote like features throughout the specification and figures.

DETAILED DESCRIPTION

Various aspects of the disclosure are described below. It should beapparent that the teachings herein may be embodied in a wide variety offorms and that any specific structure, function, or both being disclosedherein is merely representative. Based on the teachings herein oneskilled in the art should appreciate that an aspect disclosed herein maybe implemented independently of any other aspects and that two or moreof these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein. Furthermore,an aspect may comprise at least one element of a claim.

FIG. 1 illustrates several nodes of a sample communication system 100(e.g., a portion of a communication network). For illustration purposes,various aspects of the disclosure will be described in the context ofone or more access terminals, access points, and network entities thatcommunicate with one another. It should be appreciated, however, thatthe teachings herein may be applicable to other types of apparatuses orother similar apparatuses that are referenced using other terminology.For example, in various implementations access points may be referred toor implemented as base stations, NodeBs, eNodeBs, home NodeBs, homeeNodeBs, macro cells, femto cells, and so on, while access terminals maybe referred to or implemented as user equipment (UEs), mobiles, and soon.

Access points in the system 100 provide access to one or more services(e.g., network connectivity) for one or more wireless terminals (e.g.,access terminals 102 and 104) that may be installed within or that mayroam throughout a coverage area of the system 100. For example, atvarious points in time the access terminal 102 may connect to an accesspoint 106, an access point 108, or some access point in the system 100(not shown).

Certain types of access points (e.g., femto cells) may be configured tosupport different types of access modes. For example, in an open accessmode, an access point may allow any access terminal to obtain any typeof service via the access point. In a restricted (or closed) accessmode, an access point may only allow authorized access terminals toobtain service via the access point. For example, an access point mayonly allow access terminals (e.g., so called home access terminals)belonging to a certain subscriber group (e.g., a closed subscriber group(CSG)) to obtain service via access point. In a signaling-only (orhybrid) access mode, alien access terminals (e.g., non-home accessterminals, non-CSG access terminals) may only be allowed to obtainsignaling access via the access point. For example, a macro accessterminal that does not belong to a femto cell's CSG may be allowed toperform certain paging, registration, and other signaling operations atthe femto cell, but may not be allowed to obtain active mode service viathe femto cell.

Each of the access points may communicate with one or more networkentities (represented, for convenience, by a network entity 110) tofacilitate wide area network connectivity. These network entities maytake various forms such as, for example, one or more radio and/or corenetwork entities. Thus, in various implementations the network entitiesmay represent functionality such as at least one of: network management(e.g., via an operation, administration, management, and provisioningentity), call control, session management, mobility management, gatewayfunctions, interworking functions, or some other suitable networkfunctionality. Also, two of more of these network entities may beco-located and/or two or more of these network entities may bedistributed throughout a network.

The access point 106 (e.g., a femto cell) provides service for nearbyaccess terminals through the use of a service channel that operates on adesignated carrier frequency. In some cases (e.g., co-channeldeployments), this carrier frequency may be used by different types ofaccess points (e.g., femto cells and macro cells). In other cases,different types of access points may operate on different carrierfrequencies. For example, femto cells may deploy their service channelson a dedicated femto carrier frequency, while macro cells may deploytheir service channels on one or more macro carrier frequencies. In thelatter case, a femto cell may transmit beacons on each macro carrierfrequency to enable nearby access terminals operating on that carrierfrequency to find the femto cell. Thus, in either a co-channel or anon-co-channel deployment scenario, transmissions by a femto cell on agiven carrier frequency may interfere with signal reception at a nearbyaccess point that is in active communication with another access point(e.g., a macro cell or another femto cell).

The potentially interfering transmissions by an access point may takevarious forms. For example, in a co-channel deployment, a femto cell'sforward link transmissions (e.g., for the service channel) may causeinterference at nearby macro access terminals operating on the samecarrier frequency. As another example, in a deployment where a femtocell transmits beacons on a macro carrier frequency, these beacontransmissions may cause interference at nearby macro access terminalsoperating on that macro carrier frequency. In some implementations, anaccess point transmits beacons at different power levels. Here, theaccess point will normally transmit beacons at a low power level in anattempt to minimize interference caused by the beacons. However, theaccess point will regularly transmit beacons at a higher power level (ormultiple higher levels) for short periods of time to facilitateattracting access terminals from a greater distance.

The access point 106 employs transmit power control to provide a desiredarea of communication coverage for attracting and/or communicating withaccess terminals (e.g., the access terminal 102) that are authorized toreceive active mode service from the access point 106, while mitigatinginterference that transmissions by the access point 106 may have onnearby access terminals (e.g., the access terminal 104) that are notauthorized to receive active mode service from the access point 106. Forexample, the access terminal 102 may be a member of a CSG of the accesspoint 106 while the access terminal 104 is not a member of that CSG. Inthis case, it is desirable for the access point 106 to use sufficienttransmit power (e.g., for beacon and/or forward link transmissions) sothat the access terminal 102 is able to detect the presence of theaccess point 106 and/or communicate with the access point 106 from aparticular distance (e.g., throughout a building within which the accesspoint 106 is deployed). Conversely, it is preferable that thetransmissions by the access point 106 do not unduly interfere with theability of the access terminal 104 to receive signals from the accesspoint 108 (e.g., a serving macro cell for the access terminal 104).

In accordance with the teachings herein, the access point 106 may employa multi-stage transmit power control scheme. For example, the accesspoint 106 may jointly employ network listen-based power calibration(NLPC) functionality as represented by the block 112, mobile assistedrange tuning (MART) functionality as represented by the block 114, andactive mobile protection functionality as represented by the block 116.At any given point in time, transmit power is controlled (e.g.,calibrated) depending on the state of the access point 106.

In a sample implementation, these states may comprise an initialization(e.g., power-up or recalibration) state, a post-initialization state,and a state relating to the detection of the presence of an active macrouser in the vicinity of the access point 106. For example, when theaccess point 106 is powered-up, the access point 106 initially usesNLPC.

Subsequently, the access point 106 uses mobile (i.e., access terminal)assisted range tuning. For example, the access point 106 may switch tothe MART state after it collects a sufficient amount of information fromnearby mobiles. This information may be collected in different ways andmay take different forms. For example, at various points in time, theaccess point 106 will transmit information on its service channel andmay also transmit on one or more beacon channels. As a result of thesetransmissions, the access point 106 may receive messages from nearbyaccess terminals.

In some cases, a nearby access terminal (e.g., the access terminal 102)that is authorized to obtain active mode service via the access point106 may send measurement report messages to the access point 106. Thesemeasurement report messages may thus report the signal power measured atthe access terminal 102 for the femto service channel and/or the beaconchannel(s). In some cases, the access point 106 may request the accessterminal to measure channel quality on the femto service channel and/orthe beacon channel(s) and report this information back using measurementreport messages. Additionally, in some cases, the access point 106 mayrequest the access terminal to report path loss on the femto servicechannel and/or the beacon channel and report this information back usingmeasurement report messages.

In addition, in some cases, a nearby access terminal (e.g., the accessterminal 104) that is being served by another access point (e.g., theaccess point 108) or that is in idle mode may attempt to register withthe access point 106 as a result of receiving beacons or forward linksignals from the access point 106. Consequently, such an access terminalmay send registration messages to the access point 106. In some cases,the access point 106 may request that one or more of signal power,quality or path loss to be reported as a part of a registration messagefrom the access terminal 104. As discussed in more detail below, as aresult of receiving these messages, the access point 106 may determinehow to best adjust its transmit power to provide an acceptable tradeoffbetween providing adequate coverage and minimizing interference.

In the MART state, the access point 106 may continually (e.g.,periodically) update the transmit power. For example, the access point106 may acquire information from nearby access terminals (e.g., channelquality, received power, and path loss reports from home mobiles andregistration statistics of alien access terminals) and then fine tunethe transmit power on a periodic basis based on this information.

In addition, while in the MART state, the access point 106 may regularlymonitor network conditions to determine whether there has been asignificant change in network conditions (e.g., due to a change in femtocell location and/or installation/removal of access points in thevicinity). If so, the access point 106 may switch back to the networklisten-based power calibration state to update one or more power controlparameters (e.g., transmit power limits). For example, a femto cell mayperiodically perform network listen measurements and performsrecalibration if the RF environment has changed. A change in the RFenvironment may be detected by comparing previous network listenmeasurements with the new network listen measurements. If a change isdetected, transmit power may be re-calibrated by combining networklisten measurements with previously learned information from the homeaccess terminal reports and access terminal registration statistics(e.g., from preferred access terminals and/or from non-preferred accessterminal such as alien access terminals). The periodicity of makingnetwork listen measurements for recalibration may be smaller than theMART periodicity. Also, recalibration is done under events such as whenthe access points is re-powered up, when the RF environment has changed,or when the access point is explicitly directed to re-calibrate by thenetwork.

Also, while in the NLPC state or the MART state, the access point 106may regularly (e.g., continually) monitor for the presence of any nearbyactive users. For example, a femto cell may monitor for nearby activemacro users by measuring out-of-cell interference on one or more reverselink frequencies. In the event a nearby active user is detected on agiven carrier frequency, the access point 106 switches to the activemobile protection state. Here, the access point 106 may temporarilylimit its transmissions by, for example, reducing transmit power orceasing transmission on that carrier frequency. Then, upon determiningthat the user is no longer nearby or is no longer active, the accesspoint 106 returns to the previous state (e.g., NLPC or MART).

From the above, it should be appreciated that while in the NLPC state,the access point 106 may transmit using transmit power parametersdetermined by an NLPC algorithm. Conversely, while in the MART state,the access point 106 may transmit using transmit power parametersdetermined by a MART algorithm, whereby the transmit power parametersare based on messages received from at least one access terminal (e.g.,a home access terminal). In the MART state, the access point 106 willcontinue collecting messages from the at least access terminal. Inaddition, for active mobile protection, the access point 106 mayregularly monitor for other access terminals (e.g., active macro accessterminals) that may be subject to interference from the access point106.

Sample operations of the system 100 will now be described in more detailin conjunction with the flowchart of FIGS. 2 and 3. For convenience, theoperations of FIGS. 2 and 3 (or any other operations discussed or taughtherein) may be described as being performed by specific components(e.g., the components of FIG. 1 and FIG. 8). It should be appreciated,however, that these operations may be performed by other types ofcomponents and may be performed using a different number of components.It also should be appreciated that one or more of the operationsdescribed herein may not be employed in a given implementation.

As represented by block 202 of FIG. 2, initialization of an access point(e.g., a femto cell) is commenced at some point in time. For example,the access point may be powered-up, reset, or subjected to some otherprocedure that commences initialization of the access point.

As represented by blocks 204 and 206, the access point employs networklisten-based power calibration (NLPC) after initialization is commenced.In some aspects, this involves monitoring one or more channels (e.g., ona corresponding carrier frequency) to determine the correspondingchannel quality (e.g., received signal strength) as seen by the accesspoint. Here, an underlying assumption of NLPC is that the channelquality (e.g., macro channel quality) measured by the access point issimilar to that observed by an access terminal (e.g., a home accessterminal) at the edge of the access point's coverage range.

An access point may perform this monitoring using a network listenmodule (NLM) or other suitable component(s). The NLM is a subsystem ofthe access point that has mobile-like capabilities that enable theaccess point to listen for (sometimes referred to as “sniffing”) RFsignals from neighboring access points (e.g., macro access points and/orfemto access points). The access point may then measure a suitablechannel quality metric (e.g., received signal strength) based on thesesignals. From this metric, the access point may set the initial transmitpower to be used by the access point. This initial transmit power maycomprise, for example, an initial value to be used for the transmitpower or an initial range (e.g., specified by minimum and maximumlimits) within which the transmit power is to be limited.

The NLPC channel monitoring may involve acquiring different types ofsignal information depending on the type of deployment, the type ofchannel(s) being monitoring, and potentially other factors. For example,the access point may monitor the carrier frequency that carries theaccess point's service channel or the access point may monitor othercarrier frequencies that carry other types of channels (e.g., beaconchannels)

In some deployments, a femto cell transmits beacons on one or morecarrier frequencies used by other access points (e.g., macro carrierfrequencies). In this case, the femto cell may use NLPC to controltransmit power on each of these carrier frequencies to mitigate anyinterference the transmission of these beacons may have on nearby accessterminals operating on those frequencies (e.g., so-called macro accessterminals that are currently being served by a macro cell).

Beacon power may be calibrated by measuring the surrounding macronetwork's forward link (FL) channel quality using the NLM. For example,the femto cell may use the NLM to scan for pilots from the macro accesspoint(s) on each frequency and measure the corresponding pilot energy(e.g., Ecp). Using these received signal measurements and a defined(e.g., assumed) coverage range, the femto cell may adapt its beacontransmit power based on the femto cell's location in the macro network.For example, the femto cell uses lower transmit power if the femto cellis deployed at the edge of a macro cell. Conversely, the femto cell useshigher transmit power if the femto cell is deployed at (e.g., near) themacro cell site.

In so-called co-channel deployments, a femto cell is deployed on thesame carrier frequency as a macro cell. That is, the femto cell'sforward link (also referred to as the downlink) is on the same carrierfrequency as the macro cell's forward link. In this case, the femto cellmay use NLPC to control transmit power on this carrier frequency tomitigate any interference the femto cell's transmissions may have onnearby access terminals (e.g., macro access terminals) operating on thisfrequency.

Here, the femto cell's forward link transmit power may be calibrated bymeasuring the surrounding macro cells' forward link channel quality(e.g., RSSI, Ecp/Io, RSCP). The femto cell uses the macro cell RSSImeasurements and a defined coverage radius (as an input) to set theinitial transmit power. The transmit power is chosen to satisfy an idlereselection requirement. For example, the femto cell CPICH Ec/Io shouldbe better than Qqualmin for the femto cell at the edge of the coverageradius (or at a given path loss). To achieve this, the transmit powerlevel is chosen as a function of the measured macro quality (CPICH/Io)and a path loss value. Furthermore, to limit interference induced atnearby access terminals (e.g., macro access terminals), anotherpotential requirement is for the femto cell transmission to increase Ioby at most a certain fixed amount at the edge of the femto cell coveragerange (or at a given path loss). The femto cell transmit power is thenchosen to be the minimum of these two criteria. Again, this allows thefemto cell to adapt its transmit power based on its location in themacro network. The transmit power is set lower at a location where macrocell RSSI is weak as compared to a location where macro cell RSSI isstrong.

As represented by block 208 of FIG. 2, an access point also may employactive mobile protection in some implementations. For example, a femtocell's beacon transmissions may degrade the voice call quality of activemacro users in the vicinity of the femto cell. To protect these activemacro mobiles from such beacon interference, whenever the presence of anearby active macro user is detected, the femto cell temporarilythrottles (i.e., restricts) beacon transmissions.

Accordingly, an access point may regularly (e.g., continuously) monitorfor the presence of nearby active non-home access terminals (e.g.,active macro access terminals) and take action to restrict the accesspoint's transmissions until that access terminal leaves the vicinity orends the active communication. Once there are no longer any such activeaccess terminals in the vicinity of the access point, the access pointmay resume using the transmit power level dictated by the other transmitpower algorithms (e.g., NLPC or MART).

An access point may restrict its transmission in various ways. In someimplementations, the access point temporarily reduces its transmitpower. For example, the access point may temporarily reduce the maximumtransmit power limit that it uses for transmitting beacons. In someimplementations, the access point temporarily reduces the periodicity ofits transmission. For example, in a case where the access pointperiodically transmits a beacon on a given carrier frequency (e.g., whentime division multiplexing beacon transmissions on different carrierfrequencies), the access point may temporarily reduce the period of timethat a beacon is transmitted on the carrier frequency. In someimplementations, the access point temporarily ceases transmission. Forexample, the access point may temporarily cease transmitting beacons onany macro carrier frequencies that are being used to send information toa detected access terminal.

An access point may employ various techniques for restrictingtransmission on a temporary basis. In some implementations, the accesspoint restricts transmission for a defined period of time. For example,the access point may start a timer upon restricting transmission, andterminate the restriction of transmission once the timer expires. Insome implementations the access point restricts transmission until aterminating event occurs. For example, in cases where detection of anaccess terminal is based on a measured received signal strengthexceeding a threshold, the access point 104 may terminate therestriction of transmission when measured received signal strength fallsbelow a certain configurable threshold. In any of these cases, uponterminating the restriction of transmission, the access point 104 mayresume transmitting at the transmit power level and/or periodicity thatwas used prior to the restriction of transmission.

In some implementations, for robustness against channel fading, thetransmit power is reduced to a value that is inversely proportional tothe filtered RSSI. The proportionality constant is a tunable parameterused to trade-off between the amount of throttling applied to limitinterference versus the reduction in femto cell coverage caused by thethrottling.

An access point may detect the presence of an active access terminal invarious ways. Several examples for the case where the access pointcomprises a femto cell that restricts its beacon transmissions follow.

In some implementations, the femto cell detects the presence of a nearbymacro cell user by measuring received signal strength on the macro cellreverse link carrier frequency that is (or frequencies that are) pairedwith a macro cell forward link carrier frequency (or frequencies). Thismeasurement may be referred to as a received signal strength indication(RSSI). For example, the measurement of a reverse link RSSI value thatexceeds a certain expected value (e.g., a threshold) over a period oftime may serve as an indication of the presence of an active macro celluser that is receiving on the corresponding forward link frequency. Inthe absence of any active macro user in the proximity of the femto cell,the reverse link RSSI is expected to be very close to a noise floor forthe femto cell (e.g., a thermal noise level). Therefore, the rise ofRSSI above a pre-computed threshold that is based on this noise floormay be used as an indication of the presence of an active macro usernearby. The throttling may then be discontinued after a time-out or whenRSSI again falls below a defined threshold.

In some implementations, the presence of a nearby active macro cell usermay be known apriori to the access point. For example, in a case ofactive handover of an access terminal from a femto cell to a macro cell(commonly referred to as active hand-out) for a restricted user or guestuser, the femto cell will know that this access terminal is in thevicinity of the femto cell and is now being served by the macro cell.The femto cell may therefore restrict transmission (e.g., apply beaconthrottling) on the downlink carrier frequency or the set of downlinkcarrier frequencies on which the macro cell user receives informationfrom the macro network. Thus, in the case where the femto cell supportssignaling-only access mode (e.g., hybrid mode), throttling may beapplied when an alien access terminal camping on the femto cell ishanded-out to the macro cell for active mode service.

As represented by block 210 of FIG. 2, an access point may regularly(e.g., periodically) monitor for changes in channel quality to determinewhether to temporarily revert back to NLPC. For example, if there hasbeen a recent significant change in channel quality (e.g., due to achange in the location of the access point, and/or installation/removalof access points in the vicinity), the information collected for MARTmay be considered unreliable. In such a case, the access point mayswitch back to the NLPC state to reestablish initial transmit powerlimits for the access point until new MART information is acquired.

Thus, in addition to initial power setting upon initialization, the NLPCtechnique may be used for recalibration purposes to identify changes inthe RF environment due to events such as a change in an access point'slocation and adjust the transmit power accordingly. Such recalibrationmay be initiated autonomously by the access point or directed by thenetwork. Recalibration may also be initiated upon re-power-up or resetof the femto cell. After reset or re-power-up, the femto cell may firstcheck for changes in channel quality. If no significant change isdetected, the femto cell may use the transmit power that was used priorto the reset or re-power-up event. Otherwise, the femto cell may switchback to the NLPC state to reestablish initial transmit power levels.

In practice, NLPC may have certain inherent limitations. First, thedesired femto cell coverage range (e.g., beacon coverage radius), whichmay be a user input, may not be the correct estimate. For example,whether the femto cell is deployed in a small apartment or a large housemay be a priori unknown. Second, user traffic in the apartment vicinitymay vary significantly from apartment to apartment. For example, whetherthe femto cell is deployed in an apartment-unit facing a busy street ora street with very light traffic may not be known a priori. Third, NLPCassumes that the macro channel quality throughout the apartment or houseis same as that measured by the NLM at the femto cell installedlocation. In practice, however, there may be a significant RF mismatchbetween RF conditions at the femto cell and at the access terminals inthe apartment/house. Thus, NLM measurements may not truly represent theRF environment throughout the apartment/house. The RF mismatch at thefemto cell and that experienced by users at different locations in theapartment/house affects performance. For example, when placed near awindow, a femto cell detects a strong macro signal and transmits at ahigh power, which causes interference to outdoor users and at same timeis more than adequate to provide coverage inside the house, where macrochannel quality is weak.

Due to these limitations, NLPC may result in an unnecessarily high orlow transmit power level. Therefore, it is desirable to fine tune thefemto cell transmit power and its coverage for better adaptation to thedeployment scenario. Such fine tuning can be achieved through the use ofthe MART operations described in FIG. 3.

In some implementations, MART is based on channel quality reportsregarding channel quality on one or more frequencies obtained from homeaccess terminals (hereafter referred to as HAT reports) and/orstatistics of registrations performed by access terminals (e.g.,preferred access terminals or non-home access terminals such as macroaccess terminals) that are in the femto cell's coverage. Here, afterapplying NLPC, MART is performed regularly (e.g., every 24 hours, everycouple of days) by collecting HAT reports and access terminalregistration statistics. In this way, MART may be used to determineoptimal long term transmit power levels for the access point.

In some aspects, adequate coverage for home access terminals may beensured through the use of HAT reports. Based on HAT feedback, a femtocell may learn the desired coverage range (i.e., path loss at differentlocations in the building) and RF conditions in the building and thenchoose an optimal transmit power level. For example, a femto cell maytransmit beacons at a relatively higher power when deployed in a largebuilding as compared to when deployed in a small building.

In some aspects, a large number of registrations by alien accessterminals is an indication of beacon leakage outside the home.Therefore, when the number of registrations by alien access terminals isabove a certain configurable threshold, beacon power and therefore thecoverage range of the femto cell is reduced to control beaconinterference to alien access terminals.

Blocks 212-220 of FIG. 3 represent several operations that may beperformed in a sample MART implementation.

Blocks 212 and 214 represent the collection of HAT reports. Thesereports may be sent autonomously by the access terminals, or an accesspoint may request an access terminal to periodically measure and reportback channel quality. In some implementations, a change in transmitpower based on HAT reports may not be made until the access point hasreceived a sufficient number (e.g., a defined number) of HAT reports.Accordingly, the access point may continue transmitting at a power leveldesignated by NLPC or some other algorithm until the desired number ofHAT reports has been received. During this time, the access point mayaccount for active access terminals and changes in RF conditions asdiscussed above at blocks 208 and 210.

Blocks 216 and 218 represent the collection of registration statistics.These registration statistics may correspond to, for example, the numberof registrations attempts (e.g., failed registrations by alien accessterminals) made at the access point over a defined period of time. Here,once the period of time expires, the access point may count the numberof registration attempts that occurred during the period of time.Accordingly, the access point may continue transmitting at a power leveldesignated by NLPC or some other algorithm until the period of time hasexpired. During this time, the access point may account for activeaccess terminals and changes in RF conditions as discussed above atblocks 208 and 210.

As represented by block 220, the access point sets its transmit powerbased on the HAT reports and/or the registration statistics. Bycombining information from the HAT reports and registration statisticsfrom macro (and/or other femto) access terminals, the femto cell maychoose a desired transmit power setting to balance the coverage versusinterference minimization trade-off. For example, using the receivedreports, a femto cell may estimate the path loss to a home accessterminal at different locations in a building as well as the macrochannel quality (and/or received signal power) at these locations. Thefemto cell may thus learn the required coverage range and RF conditionsin the building and fine tune its transmit power accordingly. As aresult, the femto cell may automatically transmit at a relatively higherpower when deployed in a large building as compared to when it isdeployed in a small building.

In some implementations, femto cell transmit power is chosen to satisfya home access terminal coverage constraint and a macro cell userprotection constraint. For the access terminal coverage constraint, thetransmit power level is chosen such that the CPICH Echo experienced by ahome access terminal at the edge of the femto cell coverage radius(e.g., at a given path loss from the femto cell) is above a certainthreshold. For the macro cell user protection constraint, the transmitpower level is chosen to limit the impact of the femto celltransmissions on alien macro access terminals at a given path loss fromthe femto cell. To achieve this, the transmit power level is chosen suchthat femto cell interference does not exceed the total received power(Io) on the macro cell frequency by more than a certain amount at theedge of the femto cell coverage radius (e.g., at a given path loss fromthe femto cell).

As mentioned above, different implementations may or may not employ oneor more of NLPC, HAT-based MART, or registration-based MART.Accordingly, the interaction of these algorithms may depend in someaspects on which algorithms are used by the access point.

In one example of an implementation that supports an NLPC, HAT-basedMART, and registration-based MART scheme, NLPC is used to define thetransmit power limits initially used by the access point. Until asufficient number of HAT reports are acquired, the actual transmit powerused by the access point is set to a value within these limits based onthe registration statistics. Once a sufficient number of HAT reports areacquired, the access point defines new transmit power limits based onthe HAT reports. The actual transmit power used by the access point isthen set to a value within the new limits based on the registrationstatistics (e.g., the number of failed registration attempts, the numberof registration attempts received).

In another example of an implementation that supports an NLPC, HAT-basedMART, and registration-based MART scheme, NLPC is used to define thetransmit power initially used by the access point. Once a sufficientnumber of HAT reports are acquired, the access point defines transmitpower limits based on the HAT reports. The transmit power is thendefined within these limits based on the registration statistics.

In one example of an implementation that supports an NLPC and HAT-basedMART scheme, NLPC is used to define the transmit power initially used bythe access point. Once a sufficient number of HAT reports are acquired,the access point defines a transmit power level based on the HATreports.

In one example of an implementation that supports an NLPC andregistration-based MART scheme, NLPC is used to define the transmitpower limits initially used by the access point. Once the period of timefor collecting registration statistics expires, the access point definesa transmit power level within those transmit power limits based on theregistration statistics (e.g., by incrementing or decrementing thetransmit power within the limits set by NLPC). In some cases, thiscombination is used prior to the collection of a sufficient number ofHAT reports. In these cases, the transmit power control may revert backto an NLPC, HAT-based MART, and registration-based MART scheme oncesufficient HAT reports have been collected.

Referring now to the flowchart of FIGS. 4 and 5, additional detailsrelating to how NLPC may be used at an access point to set transmitpower limits for another transmit power control algorithm is described.It should be appreciated that the operations described below also may beapplicable to using NLPC to set a specific transmit power value.

As represented by block 402 of FIG. 4, the described operations beginwith initialization of the access point. Here, the access point mayprovide a mechanism to determine that initialization has commenced (or,as discussed below, that recalibration is needed) and trigger thecommencement of NLPC based on this determination.

As represented by block 404, the access point maintains informationindicative of a desired coverage range for the access point during NLPC.For example, this information may comprise a first path loss valuecorresponding to a larger coverage radius for high power beacons andsecond path loss value corresponding to a smaller coverage radius forlow power beacons. These parameters may be provisioned by the network(e.g., over the backhaul) or the access point may use certain typicalvalues. In either case, these values may be stored in a memory componentof the access point.

As represented by block 406, the access point is configured to monitorfor signals from other access points on one or more carrier frequencies(e.g., by using a network listen module). For example, in a co-channeldeployment, the access point may monitor the carrier frequency used forthe access point's service channel for signals (e.g. pilots) from otheraccess points. In a deployment where the access point transmits beaconson a carrier frequency (e.g., a macro carrier frequency) other than theaccess point's service channel carrier frequency, the access point maymonitor that carrier frequency for signals from other access points. Itshould be appreciated that the access point may monitor more than oncarrier frequency (e.g., in cases where the access point needs tocontrol transmit power on more than one carrier frequency).

As represented by block 408, the access point determines signal strengthinformation associated with the received signals. In this way, theaccess point may estimate the channel quality at the access point due totransmissions by neighboring access points. For example, in someimplementations, the access point may measure the received pilot energy(e.g., Ecp) for each macro access point operating on a given carrierfrequency. In some implementations, the access point may measure totalsignal power Io (e.g., total RSSI) along with CPICH RSCP and/or CPICHEc/Io and/or path loss for access points on a given carrier frequency.

As represented by block 410, the access point sets transmit power limitsfor another transmit power algorithm based on the determined signalstrength and the maintained coverage range information. For example, theaccess point may initially determine a nominal transmit power levelbased on the signal strength and coverage range information. The accesspoint may then define upper and lower limits based on the nominaltransmit power level (e.g., by adding a Δ to provide the upper limit andsubtracting a Δ to provide the lower limit). Two sample implementationsfor determining such a nominal transmit power value follow.

The first implementation may be employed, for example, in a deploymentwhere a femto cell transmits beacons on a macro carrier frequency thatis different from the service channel carrier frequency of the femtocell. Here, the femto cell scans for macro access point pilots anddetermines the pilot energy (Ecp_(macro)) of the strongest macro accesspoint. In addition, a high power beacon coverage radius PL_(high) and alow power beacon coverage radius PL_(low) are defined in term of pathloss for beacon transmissions as discussed above.

Different algorithms are employed for setting the transmit powerdepending on whether the monitoring results in detection of a macroaccess point. If no macro access point is detected, the nominal transmitpower (P_(low)) for the low power beacon is set to the minimum beaconpower level specified for the femto cell. In addition, the nominaltransmit power (P_(high)) for the high power beacon is set a definedamount (e.g., +Δ) higher than the low power beacon transmit power(constrained by an upper limit of the maximum beacon power levelspecified for the femto cell).

If a macro access point was detected, P_(low) is set toEcp_(macro)+PL_(low)+Hyst+EcpIor_(beacon) (constrained by the maximumand minimum beacon transmit power levels). Note that the equationsassume all quantities are in log scale, i.e., dB, dBm units. Similarly,P_(high) is set to Ecp_(macro)+PL_(high)+Hyst+EcpIor_(beacon)(constrained by the maximum and minimum beacon transmit power levels,and also constrained to be at least a defined amount (e.g., +Δ) higherthan P_(low)). Here, Hyst is a configurable parameter that controlsbeacon power relative to macro pilot energy and EcpIor_(beacon) is aconfigurable parameter representing the ratio of pilot power to thetotal power transmitted on the beacon channel. Hyst is typically chosenbased on handoff hysteresis criteria used by access terminals fordetermining when to handoff from a macro pilot to a beacon pilot. Insome aspects, the above equations may ensure that an access terminal atthe path loss edge receives sufficient power from the access point tocause the access terminal to hand-in to the access point.

The nominal transmit powers determined above (P_(high) and P_(low)) maythen be used to define corresponding transmit power limits. For example,minimum and maximum transmit power limits for the low power beacon maybe specified as P_(low)−Δ₁ and P_(low)+Δ₂, respectively. Similarly,minimum and maximum transmit power limits for the high power beacon maybe specified as P_(high)−Δ₃ and P_(high)+Δ₄, respectively.

The second implementation mentioned above may be employed, for example,in a co-channel deployment. Here, a femto cell may estimate Io (e.g., bymeasuring the total RSSI) on the forward link carrier frequency. Inaddition, the femto cell determines an Io value (Io_(withoutfemtos))corresponding to the interference contribution due to macro cells onthis carrier frequency (e.g., the interference that would exist in theabsence of any femto cells). The femto cell also maintains an Io value(Io_(this,femto)) that corresponds to the allowed additionalinterference contribution due to transmissions by the femto cell (e.g.,assuming certain loading). In addition, the femto cell maintains anEcpIo value (EcpIo_(min,femtouser)) that corresponds to the minimumdesired downlink pilot strength (CPICH Ec/Io) experienced by a homeaccess terminal of the femto cell (e.g., assuming certain loading at theedge of the femto cell coverage).

A nominal transmit power value is computed such that sufficient power isprovided for a home access terminal at the coverage edge, whilerestricting this power by the amount of allowed interference.Specifically, the transmit power level is chosen such that the femtocell CPICH Ec/Io (for a given femto cell loading) at the coverage radius(PL_(edge)) exceed EcpIo_(min,femtouser), while ensuring that theconfigured transmit power levels are within certain defined limits.

For example, a value (P_(temp1)) constrained by the allowed interferenceis set to PL_(edge)+Io_(withoutfemtos)+Io_(this,femto)−EpcIor_(femto),where EcpIor_(femto) is the ratio of pilot energy per chip to the totaltransmit power spectral density (e.g., CPICH Ec/Ior). In addition, avalue (P_(temp2)) constrained by the power needed by a femto cell useris set to PL_(edge)+Io_(withoutfemtos) (a parameter based onEcpIo_(min,femtouser), EcpIor_(femto), and a loading factor).

The nominal transmit power (P_(femto)) is then selected as the minimumof these two values (P_(temp1) and P_(temp2)) constrained by the minimumand maximum permissible values of the total femto cell transmit power.This nominal transmit power may then specify the maximum transmit power.This value may then be used to define corresponding transmit powerlimits. For example, minimum and maximum power limits for the femto celltransmission on the forward link may be specified as P_(femto)−Δ andP_(femto), respectively.

Referring now to block 412 of FIG. 5, after the transmit power limitsare defined at block 410, the access point (e.g., femto cell) employsanother power control algorithm (e.g., HAT report-based and/orregistration-based MART) to control the transmit power. For example, asdiscussed herein, a MART-based algorithm may specify a transmit powervalue within the transmit power limits defined at block 410. Asdiscussed above, until a sufficient number of HAT reports are obtained,the access point may transmit using NLPC-based limits, where the actualtransmit power value used within these limits is based on registrationstatistics. Then, once a sufficient number of HAT reports are available,new limits based on the HAT reports are provided. The actual transmitpower value used within these new limits is again based on registrationstatistics.

As represented by block 414 of FIG. 5, the access point may regularly(e.g., periodically) perform network listen measurements to determine ifNLPC recalibration is needed. Such a recalibration may be indicated, forexample, as a result of a change in the location of the access point, asa result of a movement of objects in the access point's coverage area,or as a result of a new access point being deployed in the vicinity ofthe access point. The access point may adjust the transmit power limits(e.g., by setting new values as described above) whenever a change inthe channel quality on a given carrier frequency (e.g., forward link orbeacon channel) is detected. For example, upon receiving additionalsignals on the carrier frequency, the access point may determine newsignal strength information associated with these additional signals andcompare the new signal strength information with the prior signalstrength information. If the result (e.g., difference or ratio) of thecomparison exceeds a defined threshold, the access terminal may invokeNLPC recalibration to adjust the transmit power limits.

Referring now to FIGS. 6 and 7, additional details of sampleMART-related operations that may be performed by an access point (e.g.,a femto cell) will now be described. Specifically, FIG. 6 describessample operations for a HAT report-based scheme, while FIG. 7 describessample operations for a registration-based scheme. In a typicalscenario, each of these schemes involves collecting a corresponding setof statistics (e.g., statistics regarding path loss, channel qualityfrom HAT reports or registration messages collected over a time period)and periodically updating transmit power based on the collectedstatistics.

In some aspects, the assumptions that follow may be applicable to theMART operations of FIGS. 6 and 7. First, the access point (e.g., femtocell) employs a restricted access policy or a signaling-only accesspolicy. In the latter case, alien access terminals may register with theaccess point in idle mode and camp (stay connected in idle mode) on theaccess point, but cannot get active mode service. Second, the accesspoint is able to distinguish between home access terminals and alienaccess terminals in some manner. For example, the access point may beable to distinguish access terminals based on their unique identifierssuch as International Mobile Subscriber Identity (IMSI) or ElectronicSerial Number (ESN). This information may be provisioned by the networkto the access point or may be learned by the access point. For example,when an alien access terminal camping on a femto cell originates orreceives a call, the access terminal will be re-directed to a macroaccess point for active mode service. The femto cell may thereforerecord the IMSIs of such access terminals to classify them as alienaccess terminals. Conversely, the IMSIs of mobiles that receive activeservice from the femto cell may be recorded and classified as homeaccess terminals.

Referring initially to FIG. 6, as represented by blocks 602 and 604, anaccess point will transmit voice and/or data on a forward link and maytransmit beacons on one or more beacon channels as described herein. Forexample, in a co-channel deployment, a femto cell may transmit pilotsand service channel information on a carrier frequency that is sharedwith one or more macro cells. Also, in a non-co-channel deployment, afemto cell may transmit service channel information on a femto carrierfrequency and transmit beacons on one or more macro carrier frequencies.

As represented by block 606, the access point receives messagesindicative of channel quality on the forward link and/or a beaconchannel. For example, the access point may receive measurement reportsfrom a home access terminal as the access terminal moves throughout thecoverage area of the access point. These measurement reports may includemeasurements the access terminal made on the forward link carrierfrequency and/or on a macro carrier frequency or frequencies.

These reports may be triggered in various ways. In some cases, an accessterminal may autonomously send a measurement report based on theoccurrence of an event at the access terminal (e.g., a measurementreporting event). In some cases, the access point may request the accessterminal to send measurement reports. For example, a femto cell mayrequest an active home access terminal to send forward link channelquality reports corresponding to the femto cell and neighboring macrocells as well as other femto cells. Here, the request may specify thatthe reports are to be sent repeatedly (e.g., periodically such as everyfew seconds or minutes).

Measurement report messages may take various forms. For example, reportson the forward link service channel may be requested using periodicpilot strength measurement messaging (periodic PSMM) mechanisms incdma2000 1xRTT femtocells. Similarly, reports on a frequency differentfrom the service frequency may be requested using candidate frequencysearch (CFS) request and report mechanisms in cdma2000 1xRTT femtocells.

In UMTS, a femto cell may configure an event elX through the use ofmeasurement control messages. Such a message may be configured, forexample, with the identifiers (e.g., primary scrambling codes) of themacro cells and femto cells (including the requester) to be reported.The message also may specify the parameters to be reported (e.g., CPICHEc/Io and CPICH RSCP).

The collection of HAT reports on the service channel and thebeacon/macro channel may be synchronized. For example, beacon channelmeasurements may be requested within few hundred milliseconds or a fewseconds of the forward link service channel measurements in order tocorrelate the information across frequencies and improve performance.For example, if the path loss to an access terminal at a given locationis being determined based on a report of a femto cell's service channeland the channel conditions are being determined based on a report of amacro channel that the access terminal sent from that location, it isdesirable that these reports be correlated in time so that the correctpath loss is matched up with the reported channel conditions.

The information from the measurement reports may be processed in somecases. For example, the access point may store statistics (e.g., averageEcp/Io, average Io) based on the measurements. Also, filtering may beemployed to ensure that multiple reports from a stationary accessterminal do not bias the overall statistics. Also, filtering may beapplied to ensure that information reported by an access terminal whileor prior to being handed-over to another access point is not included inthe statistics.

Depending on the technology and access terminal capabilities, additionalinformation (e.g., path loss values) may be reported by an accessterminal and stored in a database of the access point in conjunctionwith learning the RF environment in the building and adjusting transmitpower accordingly. Also, the home access terminal reports may becollected in idle mode, if supported by the access terminal.

As represented by block 608 of FIG. 6, the access point controls itstransmit power based on the messages received at block 606. For example,a femto cell may set a transmit power value or set transmit power limits(e.g., minimum and maximum limits) for its forward link and/or for abeacon channel. Two sample implementations for setting transmit powerlimits in this manner follow.

The first implementation may be employed, for example, in a deploymentwhere a femto cell transmits beacons on a macro carrier frequency thatis different from the service channel carrier frequency of the femtocell. For the femto forward link service channel, the femto cellcollects the following information from the measurement reports: Pilotstrength (Ecp/Io) of the femto cell forward link, Total received power(Io) measured by the access terminal. For the macro/beacon channel, thefemto cell collects the following information from the measurementreports: Ecp/Io of the beacon forward link, Ecp/Io of macro accesspoints, and total received power on the macro channel.

The femto cell also determines the path losses between the femto celland different locations from which the home access terminal sent themeasurement reports and computes statistics (e.g., median path loss,maximum path loss, or the cumulative distribution function (CDF)) onthese path losses. For example, from the femto cell's forward linkservice channel Ecp/Io and the Io reported in the PSMM, Ecp_(rx) (i.e.,pilot energy received from the femto cell) can be computed. Using thisinformation, the path loss is estimated as PL=Ecp_(tx)−Ecp_(rx), whereEcp_(tx) is the transmitted pilot energy which is known to the femtocell. Note that instead of using the forward link service channelinformation, the path loss may instead be estimated using beacon/macrochannel information if the beacon pilot strength is reported in the CFSreport.

A path loss value is computed for each home access terminal report.Thus, the femto cell learns the path loss to the access terminal at thetime when the home access terminal report was sent. Corresponding toeach of these path loss values, the femto cell also learns the macrochannel quality from the home access terminal reports. For example, thepath loss can be learned from a PSMM and the macro quality can belearned from a CFS report received within a short duration of receivingthe PSMM.

The low power and high power beacon coverage radius (PL_(low) andPL_(high)) in terms of path loss is estimated from the path lossstatistics. For example, PL_(low) is chosen as the median value andPL_(high) is chosen as the maximum value. Alternatively, PL_(low) andPL_(high) can be chosen as certain defined percentages value on the pathloss CDF such that satisfactory coverage can be achieved. These definedpercentages are configurable parameters that may be provisioned, forexample, by the network. In some other case, PL_(low) can be chosenrelative (e.g. 5 dB below) to PL_(high), which can be chosen as themaximum path loss value. Note that these PL_(low) and PL_(high) pathloss parameters may be different from the path loss parameters describedabove for NLPC.

Nominal transmit power levels are then computed for the low and highpower beacons by determining the transmit power needed to provide adesired level of coverage at all or a subset of the locations from whichreports were received (i.e., corresponding to the computed path losses).For example, for the lower power beacon, all home access terminalreports that have path loss smaller than PL_(low) [dB] are denoted asS_(low,cov). Also, the Ecp_(macro) (i.e., the pilot energy of the bestmacro cell for each report in this set) is determined based on the macroEcp/Io and Io on the macro carrier frequency. The rest of the operationsare performed on reports in this set. Let N be the number of reports inthis set and let PL(i) and Ecp_(macro)(i) denote the path loss value andthe best macro cell's pilot energy obtained from the ith report in thisset. Now within the permissible power range [P_(min), P_(max)] thatdepends on femto cell capabilities, find a minimum power value (say,P_(temp)) such that the coverage criteria P_(temp)=Ecp_(macro)(i)PL(i)+Hyst−EcpIor_(beacon) is satisfied for all or a subset of thereports out of the N reports. Thus, this calculation is similar to thecorresponding equation described above at block 410 for thenon-co-channel scenario. Here, the degree of coverage achieved using lowpower beacon can be controlled by choosing all or a subset of the HATreports. The nominal low power beacon transmit power levelP_(low,normal) [dBm] is then set equal to P_(temp) [dBm]. Operationssimilar to the above are also performed for the high power beacon toobtain P_(high,nominal) [dBm].

If applicable, the low and high transmit power limits are then set bysubtracting and adding deltas to the nominal values. For example, forthe low power beacon, the minimum and maximum transmit power limits areP_(low,normal)−Δ₁ and P_(low,normal)−Δ₂, respectively. As one example,the deltas may be on the order of 5 dB or 10 dB.

The second implementation mentioned above may be employed, for example,in a co-channel deployment. Here, a femto cell estimates the desiredcoverage range for femto cell downlink transmissions and computestransmit power limits based on HAT reports.

For the coverage range estimation, the femto cell computes statistics(e.g., median, max or the cumulative distribution function (CDF)) of thepath losses learned from the HAT reports. As above, the path losses arefrom the femto cell to the home access terminal for each reportinglocation. The femto cell then computes the path loss value PL_(edge)from the path loss statistics. For example, PL_(edge) can be set to themaximum path loss value or relative to maximum path loss value (e.g.,certain dB below maximum path loss value) or corresponding to a certaindefined percentage value of the path loss CDF that can providesatisfactory coverage or a defined quantity of the path loss values(corresponding to the reporting locations) that are to be covered by thefemto cell transmissions.

A nominal transmit power level is then computed by determining thetransmit power needed to provide a desired level of coverage at all or acertain defined subset of locations from which reports were received(i.e., as indicated by path losses less than PL_(edge)). For each HATreport, a nominal transmit power with a macro constraint(P_(nominal,temp1(i))) is set toPL_((i))+Io_(withoutfemtos(i))+Io_(this,femto)−EcpIor_(femto), wherePL_((i)) is the path loss for the i^(th) report. In addition, for eachHAT report, a nominal transmit power with a femto constraint(P_(nominal,temp2(i))) is set to PL_((i))+Io_(withoutfemtos(i))+(aparameter based on EcpIo_(min,femtouser), EcpIor_(femto), and a loadingfactor). Thus, these calculations are similar to the correspondingequations described above at block 410 for the co-channel scenario.

For each HAT report, another nominal transmit power(P_(nominal,temp3(i))) is then selected as the minimum of these twovalues (P_(nominal,temp1(i)) and P_(nominal,temp2(i))). The nominaltransmit power (P_(nominal)) is then computed using statistics of theset P_(nominal,temp3(i)). For example, P_(nominal) is set to the maximumof P_(nominal,temp3(i)) over all reports or chosen as the minimumtransmit power value out of all P_(nominal,temp3(i)) values such thatthe femto cell can provide coverage to all or a subset of the locationsfrom which the HAT reports were received. The value P_(nominal) isconstrained by the minimum and maximum permissible values of the totalfemto cell transmit power. This nominal value may then be used to definecorresponding transmit power limits, if applicable. For example, minimumand maximum transmit power limits for the femto cell transmission on theforward link may be specified as P_(nominal)−Δ₁ and P_(nominal)+Δ₂,respectively.

Referring now to FIG. 7, operations relating to determining a transmitpower value based on registrations will now be described. As representedby blocks 702 and 704, the access point will transmit voice and/or dataon a forward link and may transmit beacons on one or more beaconchannels as described herein (e.g., as described above at blocks 602 and604). It should be noted that in implementations where MART employs bothHAT reports and registrations, the operations of blocks 706-710 maysimply follow the operations of block 608 of FIG. 6.

As represented by block 702, at various points in time, the access pointmay receive registration messages from one or more access terminals(e.g., alien access terminals). For example, upon receiving a beaconfrom a femto cell on a macro carrier frequency, a macro access terminalmay attempt to register at the femto cell (e.g., by sending a messagethat requests registration). Similarly, upon receiving a pilot from afemto cell on a shared femto and macro carrier frequency, a macro accessterminal may attempt to register at the femto cell. Thus, in thesecases, a registration message is triggered due to beacon or pilotdetection by the macro access terminal.

Upon receiving a registration message, the access point determineswhether to accept or reject the request for registration. To the end,the access point may determine whether the access terminal is authorizedto receive active mode service via the access point. For example, afemto cell may determine whether the access terminal is a home accessterminal or an alien access terminal. This determination may be based,for example, on access control at the femto cell. If the access terminalis not allowed access (e.g., the registration attempt is rejected), theaccess point may increment a counter maintained for the currentcollection time period.

The access point may maintain such registration statistics correspondingto different transmit powers. For example, if a registration attempt wastriggered by a beacon transmission, the access point may classify theregistration attempt as resulting from a low power beacon or a highpower beacon. Thus, registration counters for low and high power may beused to fine tune low and high power levels, respectively. For example,the high or low beacon transmit power may be adjusted based only onthose registration attempts that were triggered by corresponding high orlow power beacons. An access point may distinguish whether registrationwas triggered due to beacon detection or detection of the access point'sforward link signal using a reverse mapping of the channel hashingfunction. Typically, access terminals “hash”, i.e., idle on one of theseveral macro frequencies based on their IMSI and a channel hashingfunction as specified in the relevant communication standard. The accesspoint can use the IMSI reported by the access terminal in theregistration request and back compute using the channel hashing functionwhere the access terminal was hashing prior to sending the registrationrequest. If the hashing frequency is a beacon frequency, then the accesspoint can determine that this registration was triggered due to beacondetection. Otherwise, the registration is determined to be triggered byforward link signal detection.

An access point may estimate that a given registration attempt wastriggered by a low or high power beacon based on the transmit powerlevel that was in use T_(reg) seconds prior to receiving theregistration attempt. Typically, an access terminal registration processis of the order of a second or so. Therefore, the T_(reg) parameter ischosen accordingly.

As represented by block 708, in some implementations, the access pointmay classify the access terminals that sent the registration messagesinto a set of defined access terminal types. For example, the accesspoint may determine whether an access terminal is a neighboring alienaccess terminal (relative to the access point) or a non-neighboringalien access terminal. The access point may then maintain separatecounts for the different types of access terminals for the currentcollection time period.

Such a classification scheme allows an access point to provide differentlevels of protection from access point interference to neighboringaccess terminals as compared to non-neighboring access terminals. Forexample, since neighboring access terminals will be affected by accesspoint interference for a longer duration, transmit power should bereduced even if very few neighboring access terminal registrations areobserved.

The classification of access terminals may be performed in various ways.An alien access terminal may be classified as a neighbor by tracking howoften (e.g., K days out of past L days) it registers and/or how long(e.g., a few hours) it stays in the coverage of the access point. Analien access terminal that regularly registers with the access pointand/or stays in its coverage for a certain duration may be classified asa neighbor. An access point may determine how long an alien accessterminal stays in the coverage of the access point by, for example,requesting such an access terminal to periodically register with theaccess point or acknowledge its presence by responding to a pagemessage.

In view of the above, it may be expected that a neighboring alien accessterminal (e.g., an access terminal belonging to a neighbor of a femtocell owner) would be camped on the access point for a longer amount oftime than a non-neighboring alien access terminal (e.g., an accessterminal belonging to a pedestrian or passenger in a car that is justpassing by the femto cell). Consequently, the classification of theaccess terminal may be based on a period of time that an access terminalhas camped on the access point.

In addition, it may be expected that a neighboring alien access terminalwould attempt to register at the access point more frequently than anon-neighboring alien access terminal. Consequently, the classificationof the access terminal may be based on a quantity of registrationattempts that an access terminal has made at the access point over agiven period of time.

The registration statistics may be generated in various ways. Forexample, rather than summing all registration attempts, differentweights may be applied to neighboring vs. non-neighboring registrationsand also for neighbors that register more frequently to determine thetotal registration count.

As represented by block 710, the access point controls its transmitpower based on the registration messages received at block 706. Forexample, transmit power may be updated (e.g., increased or decreased bya defined amount) relative to the currently used power level based onthe registration statistics from the last registration collection timeperiod. In addition, as discussed herein, the selected transmit powerlevel may be restricted by applicable transmit power limits (e.g., asspecified at block 608 of FIG. 6 based on HAT reports).

In some implementations, the number of failed registration attempts iscompared with a threshold. For example, if the number of registrationattempts is greater than the threshold (e.g., thereby indicating beaconleakage outside of the building), the transit power is reduced.Conversely, if the number of registration attempts is less than or equalto the threshold (e.g., thereby indicating no beacon leakage outside ofthe building), the transmit power is increased.

In cases where statistics are maintained for different access terminaltypes (e.g., neighboring and non-neighboring alien access terminals),each set of statistics may be compared to a corresponding threshold. Thedecision on how to adjust the transmit power may then be made based onone or more of these comparisons.

In cases where statistics are maintained for different transmit powerlevels (e.g., high and low power beacons), each set of statistics may becompared to a corresponding threshold. The decision on how to adjust agiven one of these transmit power levels may then be made based on thecorresponding comparison.

In some implementations the amount of the transmit power adjustment isbased on a comparison of the registration statistics to one or moreparameters. For example, the number of rejected registrations may becompared (e.g., by determining a difference or ratio) with a threshold(e.g., the threshold discussed above). The magnitude of this comparison(e.g., the magnitude of the difference or the magnitude of the ratio)may then be used to specify the magnitude of the transmit poweradjustment (e.g., a step-up value or a step-down value). In someimplementations, this operation may be performed through the use ofcurves or tables that map the comparison values (differences or ratios)to step-up and step down values. Such a mapping may be constrained byminimum and maximum allowed step-up and step-down limits.

The transmit power control schemes described herein may be implementedin a variety of ways in different implementations. For example, theteachings herein may be employed to control transmit power on varioustypes of channels (e.g., not just on beacon and service channels).Similarly, transmit power may be controlled based on information (e.g.,Ec, i.e., energy per chip on a certain channel) obtained from varioustypes of channels (e.g., not just from beacon and service channels).

An access point may transmit beacons on a single frequency or onmultiple frequencies. If beacons are transmitted on multiplefrequencies, the techniques described above may be applied on eachfrequency to determine the transmit power level on that frequency.Alternately, the same transmit power may be used on differentfrequencies or an average power level across different frequencies maybe used or the transmit power level across different frequencies may beset in proportion to the macro signal strength measured on thesefrequencies by the access point (e.g., using the network listen module).

The above algorithms may be applied with some modifications to femtocells with different access policies. For femto cells with open access,the registration limits for alien access terminals may be higher thanfor femto cells with restricted or signaling-only access. Theregistration limits may be chosen based on field trials and consideringdeployment scenarios such as dense urban areas or suburban areas.

In addition to registration counts, a femto cell may use the number ofneighboring mobiles to fine tune transmit power. For example, if thenumber of neighboring access terminals detected by the femto cell isabove a certain threshold, the transmit power is reduced, otherwise itis increased.

The step-up and step-down sizes described herein may be selected invarious ways. For example, step-up and step-down sizes may be chosendifferently for low and high power beacons. In addition, the step-up andstep-down sizes may be chosen as a function of the number ofregistrations counted and the registration limit. For example, if thenumber of registrations counted exceeds the registration limit by 100%,transmit power is reduced by Δ_(low,down), but if the number ofregistrations exceeds the registration limit by only 25%, the transmitpower is reduced by Δ_(low,down)/4.

FIG. 8 illustrates several sample components (represented bycorresponding blocks) that may be incorporated into nodes such as anaccess point 802 (e.g., corresponding to the access point 106 of FIG. 1)to perform transmit power control-related operations as taught herein.The described components also may be incorporated into other nodes in acommunication system. For example, other nodes in a system may includecomponents similar to those described for the access point 802 toprovide similar functionality. Also, a given node may contain one ormore of the described components. For example, an access point maycontain multiple transceiver components that enable the access point tooperate on multiple carriers and/or communicate via differenttechnologies.

As shown in FIG. 8, the access point 802 includes a transceiver 804 forcommunicating with other nodes. The transceiver 804 includes atransmitter 806 for sending signals (e.g., data, beacons, messages) onone or more carrier frequencies and a receiver 808 for receiving signals(e.g., beacons, messages, registration messages, pilot signals,measurement reports, repeatedly monitoring for signals) on one or morecarrier frequencies.

The access point 802 also includes a network interface 810 forcommunicating with other nodes (e.g., network entities). For example,the network interface 810 may be configured to communicate with one ormore network entities via a wire-based or wireless backhaul. In someaspects, the network interface 810 may be implemented as a transceiver(e.g., including transmitter and receiver components) configured tosupport wire-based or wireless communication. Accordingly, in theexample of FIG. 8, the network interface 810 is shown as including atransmitter 812 and a receiver 814.

The access point 802 includes other components that may be used inconjunction with transmit control-related operations as taught herein.For example, the access point 802 includes a transmit power controller816 for controlling transmit power of the access point 802 (e.g.,controlling transmit power based on received messages, identifyingchannel quality, setting at least one limit for transmit power,determining that an access terminal is actively receiving information,restricting transmission, setting transmit power to an initial value,defining transmit power limits, setting transmit power to a new value,temporarily restricting transmit power, determining a plurality of pathlosses, determining signal strength information, setting transmit powerlimits for a transmit power algorithm, determining that aninitialization procedure has commenced, triggering the setting oftransmit power limits, determining whether/that there has been a changein channel quality, adjusting transmit power limits, recalibratingtransmit power) and for providing other related functionality as taughtherein. In some implementations, some of the functionality of thetransmit power controller 816 may be implemented in the receiver 808.The access point 802 also may include a communication controller 818 forcontrolling communications by the access point 802 (e.g., sending andreceiving messages) and for providing other related functionality astaught herein. Also, the access point 802 includes a memory component820 (e.g., including a memory device) for maintaining information (e.g.,information indicative of a desired coverage range, HAT reportinformation, registration statistics, and so on).

For convenience, the access point 802 is shown in FIG. 8 as includingcomponents that may be used in the various examples described herein. Inpractice, the functionality of one or more of these blocks may bedifferent in different embodiments. For example, the functionality ofblock 816 may be different in a deployment where femto cells and macrocells share a carrier frequency as compared to a deployment where femtocells and macro cells use different carrier frequencies.

The components of FIG. 8 may be implemented in various ways. In someimplementations the components of FIG. 8 may be implemented in one ormore circuits such as, for example, one or more processors and/or one ormore ASICs (which may include one or more processors). Here, eachcircuit (e.g., processor) may use and/or incorporate data memory forstoring information or executable code used by the circuit to providethis functionality. For example, some of the functionality representedby blocks 804 and 810, and some or all of the functionality representedby blocks 816-820 may be implemented by a processor or processors of anaccess point and data memory of the access point (e.g., by execution ofappropriate code and/or by appropriate configuration of processorcomponents).

As discussed above, in some aspects the teachings herein may be employedin a network that includes macro scale coverage (e.g., a large areacellular network such as a 3G network, typically referred to as a macrocell network or a WAN) and smaller scale coverage (e.g., aresidence-based or building-based network environment, typicallyreferred to as a LAN). As an access terminal (AT) moves through such anetwork, the access terminal may be served in certain locations byaccess points that provide macro coverage while the access terminal maybe served at other locations by access points that provide smaller scalecoverage. In some aspects, the smaller coverage nodes may be used toprovide incremental capacity growth, in-building coverage, and differentservices (e.g., for a more robust user experience).

In the description herein, a node (e.g., an access point) that providescoverage over a relatively large area may be referred to as a macroaccess point while a node that provides coverage over a relatively smallarea (e.g., a residence) may be referred to as a femto access point. Itshould be appreciated that the teachings herein may be applicable tonodes associated with other types of coverage areas. For example, a picoaccess point may provide coverage (e.g., coverage within a commercialbuilding) over an area that is smaller than a macro area and larger thana femto area. In various applications, other terminology may be used toreference a macro access point, a femto access point, or other accesspoint-type nodes. For example, a macro access point may be configured orreferred to as an access node, base station, access point, eNodeB, macrocell, and so on. Also, a femto access point may be configured orreferred to as a Home NodeB, Home eNodeB, access point base station,femto cell, and so on. In some implementations, a node may be associatedwith (e.g., referred to as or divided into) one or more cells orsectors. A cell or sector associated with a macro access point, a femtoaccess point, or a pico access point may be referred to as a macro cell,a femto cell, or a pico cell, respectively.

FIG. 9 illustrates a wireless communication system 900, configured tosupport a number of users, in which the teachings herein may beimplemented. The system 900 provides communication for multiple cells902, such as, for example, macro cells 902A-902G, with each cell beingserviced by a corresponding access point 904 (e.g., access points904A-904G). As shown in FIG. 9, access terminals 906 (e.g., accessterminals 906A-906L) may be dispersed at various locations throughoutthe system over time. Each access terminal 906 may communicate with oneor more access points 904 on a forward link (FL) and/or a reverse link(RL) at a given moment, depending upon whether the access terminal 906is active and whether it is in soft handoff, for example. The wirelesscommunication system 900 may provide service over a large geographicregion. For example, macro cells 902A-902G may cover a few blocks in aneighborhood or several miles in a rural environment.

FIG. 10 illustrates an exemplary communication system 1000 where one ormore femto access points are deployed within a network environment.Specifically, the system 1000 includes multiple femto access points 1010(e.g., femto access points 1010A and 1010B) installed in a relativelysmall scale network environment (e.g., in one or more user residences1030). Each femto access point 1010 may be coupled to a wide areanetwork 1040 (e.g., the Internet) and a mobile operator core network1050 via a DSL router, a cable modem, a wireless link, or otherconnectivity means (not shown). As will be discussed below, each femtoaccess point 1010 may be configured to serve associated access terminals1020 (e.g., access terminal 1020A) and, optionally, other (e.g., hybridor alien) access terminals 1020 (e.g., access terminal 1020B). In otherwords, access to femto access points 1010 may be restricted whereby agiven access terminal 1020 may be served by a set of designated (e.g.,home) femto access point(s) 1010 but may not be served by anynon-designated femto access points 1010 (e.g., a neighbor's femto accesspoint 1010).

FIG. 11 illustrates an example of a coverage map 1100 where severaltracking areas 1102 (or routing areas or location areas) are defined,each of which includes several macro coverage areas 1104. Here, areas ofcoverage associated with tracking areas 1102A, 1102B, and 1102C aredelineated by the wide lines and the macro coverage areas 1104 arerepresented by the larger hexagons. The tracking areas 1102 also includefemto coverage areas 1106. In this example, each of the femto coverageareas 1106 (e.g., femto coverage areas 1106B and 1106C) is depictedwithin one or more macro coverage areas 1104 (e.g., macro coverage areas1104A and 1104B). It should be appreciated, however, that some or all ofa femto coverage area 1106 may not lie within a macro coverage area1104. In practice, a large number of femto coverage areas 1106 (e.g.,femto coverage areas 1106A and 1106D) may be defined within a giventracking area 1102 or macro coverage area 1104. Also, one or more picocoverage areas (not shown) may be defined within a given tracking area1102 or macro coverage area 1104.

Referring again to FIG. 10, the owner of a femto access point 1010 maysubscribe to mobile service, such as, for example, 3G mobile service,offered through the mobile operator core network 1050. In addition, anaccess terminal 1020 may be capable of operating both in macroenvironments and in smaller scale (e.g., residential) networkenvironments. In other words, depending on the current location of theaccess terminal 1020, the access terminal 1020 may be served by a macrocell access point 1060 associated with the mobile operator core network1050 or by any one of a set of femto access points 1010 (e.g., the femtoaccess points 1010A and 1010B that reside within a corresponding userresidence 1030). For example, when a subscriber is outside his home, heis served by a standard macro access point (e.g., access point 1060) andwhen the subscriber is at home, he is served by a femto access point(e.g., access point 1010A). Here, a femto access point 1010 may bebackward compatible with legacy access terminals 1020.

A femto access point 1010 may be deployed on a single frequency or, inthe alternative, on multiple frequencies. Depending on the particularconfiguration, the single frequency or one or more of the multiplefrequencies may overlap with one or more frequencies used by a macroaccess point (e.g., access point 1060).

In some aspects, an access terminal 1020 may be configured to connect toa preferred femto access point (e.g., the home femto access point of theaccess terminal 1020) whenever such connectivity is possible. Forexample, whenever the access terminal 1020A is within the user'sresidence 1030, it may be desired that the access terminal 1020Acommunicate only with the home femto access point 1010A or 1010B.

In some aspects, if the access terminal 1020 operates within the macrocellular network 1050 but is not residing on its most preferred network(e.g., as defined in a preferred roaming list), the access terminal 1020may continue to search for the most preferred network (e.g., thepreferred femto access point 1010) using a better system reselection(BSR) procedure, which may involve a periodic scanning of availablesystems to determine whether better systems are currently available andsubsequently acquire such preferred systems. The access terminal 1020may limit the search for specific band and channel. For example, one ormore femto channels may be defined whereby all femto access points (orall restricted femto access points) in a region operate on the femtochannel(s). The search for the most preferred system may be repeatedperiodically. Upon discovery of a preferred femto access point 1010, theaccess terminal 1020 selects the femto access point 1010 and registerson it for use when within its coverage area.

Access to a femto access point may be restricted in some aspects. Forexample, a given femto access point may only provide certain services tocertain access terminals. In deployments with so-called restricted (orclosed) access, a given access terminal may only be served by the macrocell mobile network and a defined set of femto access points (e.g., thefemto access points 1010 that reside within the corresponding userresidence 1030). In some implementations, an access point may berestricted to not provide, for at least one node (e.g., accessterminal), at least one of: signaling, data access, registration,paging, or service.

In some aspects, a restricted femto access point (which may also bereferred to as a Closed Subscriber Group Home NodeB) is one thatprovides service to a restricted provisioned set of access terminals.This set may be temporarily or permanently extended as necessary. Insome aspects, a Closed Subscriber Group (CSG) may be defined as the setof access points (e.g., femto access points) that share a common accesscontrol list of access terminals.

Various relationships may thus exist between a given femto access pointand a given access terminal. For example, from the perspective of anaccess terminal, an open femto access point may refer to a femto accesspoint with unrestricted access (e.g., the femto access point allowsaccess to any access terminal). A restricted femto access point mayrefer to a femto access point that is restricted in some manner (e.g.,restricted for access and/or registration). A home femto access pointmay refer to a femto access point on which the access terminal isauthorized to access and operate on (e.g., permanent access is providedfor a defined set of one or more access terminals). A hybrid (or guest)femto access point may refer to a femto access point on which differentaccess terminals are provided different levels of service (e.g., someaccess terminals may be allowed partial and/or temporary access whileother access terminals may be allowed full access). An alien femtoaccess point may refer to a femto access point on which the accessterminal is not authorized to access or operate on, except for perhapsemergency situations (e.g., 911 calls).

From a restricted femto access point perspective, a home access terminalmay refer to an access terminal that is authorized to access therestricted femto access point installed in the residence of that accessterminal's owner (usually the home access terminal has permanent accessto that femto access point). A guest access terminal may refer to anaccess terminal with temporary access to the restricted femto accesspoint (e.g., limited based on deadline, time of use, bytes, connectioncount, or some other criterion or criteria). An alien access terminalmay refer to an access terminal that does not have permission to accessthe restricted femto access point, except for perhaps emergencysituations, for example, such as 911 calls (e.g., an access terminalthat does not have the credentials or permission to register with therestricted femto access point).

For convenience, the disclosure herein describes various functionalityin the context of a femto access point. It should be appreciated,however, that a pico access point may provide the same or similarfunctionality for a larger coverage area. For example, a pico accesspoint may be restricted, a home pico access point may be defined for agiven access terminal, and so on.

The teachings herein may be employed in a wireless multiple-accesscommunication system that simultaneously supports communication formultiple wireless access terminals. Here, each terminal may communicatewith one or more access points via transmissions on the forward andreverse links. The forward link (or downlink) refers to thecommunication link from the access points to the terminals, and thereverse link (or uplink) refers to the communication link from theterminals to the access points. This communication link may beestablished via a single-in-single-out system, amultiple-in-multiple-out (MIMO) system, or some other type of system.

A MIMO system employs multiple (N_(T)) transmit antennas and multiple(N_(R)) receive antennas for data transmission. A MIMO channel formed bythe N_(T) transmit and N_(R) receive antennas may be decomposed intoN_(S) independent channels, which are also referred to as spatialchannels, where N_(S)≦min{N_(T), N_(R)}. Each of the N_(S) independentchannels corresponds to a dimension. The MIMO system may provideimproved performance (e.g., higher throughput and/or greaterreliability) if the additional dimensionalities created by the multipletransmit and receive antennas are utilized.

A MIMO system may support time division duplex (TDD) and frequencydivision duplex (FDD). In a TDD system, the forward and reverse linktransmissions are on the same frequency region so that the reciprocityprinciple allows the estimation of the forward link channel from thereverse link channel. This enables the access point to extract transmitbeam-forming gain on the forward link when multiple antennas areavailable at the access point.

FIG. 12 illustrates a wireless device 1210 (e.g., an access point) and awireless device 1250 (e.g., an access terminal) of a sample MIMO system1200. At the device 1210, traffic data for a number of data streams isprovided from a data source 1212 to a transmit (TX) data processor 1214.Each data stream may then be transmitted over a respective transmitantenna.

The TX data processor 1214 formats, codes, and interleaves the trafficdata for each data stream based on a particular coding scheme selectedfor that data stream to provide coded data. The coded data for each datastream may be multiplexed with pilot data using OFDM techniques. Thepilot data is typically a known data pattern that is processed in aknown manner and may be used at the receiver system to estimate thechannel response. The multiplexed pilot and coded data for each datastream is then modulated (i.e., symbol mapped) based on a particularmodulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM) selected for thatdata stream to provide modulation symbols. The data rate, coding, andmodulation for each data stream may be determined by instructionsperformed by a processor 1230. A data memory 1232 may store programcode, data, and other information used by the processor 1230 or othercomponents of the device 1210.

The modulation symbols for all data streams are then provided to a TXMIMO processor 1220, which may further process the modulation symbols(e.g., for OFDM). The TX MIMO processor 1220 then provides N_(T)modulation symbol streams to N_(T) transceivers (XCVR) 1222A through1222T. In some aspects, the TX MIMO processor 1220 applies beam-formingweights to the symbols of the data streams and to the antenna from whichthe symbol is being transmitted.

Each transceiver 1222 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transceivers 1222A through 1222T are thentransmitted from N_(T) antennas 1224A through 1224T, respectively.

At the device 1250, the transmitted modulated signals are received byN_(R) antennas 1252A through 1252R and the received signal from eachantenna 1252 is provided to a respective transceiver (XCVR) 1254Athrough 1254R. Each transceiver 1254 conditions (e.g., filters,amplifies, and downconverts) a respective received signal, digitizes theconditioned signal to provide samples, and further processes the samplesto provide a corresponding “received” symbol stream.

A receive (RX) data processor 1260 then receives and processes the N_(R)received symbol streams from N_(R) transceivers 1254 based on aparticular receiver processing technique to provide N_(T) “detected”symbol streams. The RX data processor 1260 then demodulates,deinterleaves, and decodes each detected symbol stream to recover thetraffic data for the data stream. The processing by the RX dataprocessor 1260 is complementary to that performed by the TX MIMOprocessor 1220 and the TX data processor 1214 at the device 1210.

A processor 1270 periodically determines which pre-coding matrix to use(discussed below). The processor 1270 formulates a reverse link messagecomprising a matrix index portion and a rank value portion. A datamemory 1272 may store program code, data, and other information used bythe processor 1270 or other components of the device 1250.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 1238,which also receives traffic data for a number of data streams from adata source 1236, modulated by a modulator 1280, conditioned by thetransceivers 1254A through 1254R, and transmitted back to the device1210.

At the device 1210, the modulated signals from the device 1250 arereceived by the antennas 1224, conditioned by the transceivers 1222,demodulated by a demodulator (DEMOD) 1240, and processed by a RX dataprocessor 1242 to extract the reverse link message transmitted by thedevice 1250. The processor 1230 then determines which pre-coding matrixto use for determining the beam-forming weights then processes theextracted message.

FIG. 12 also illustrates that the communication components may includeone or more components that perform transmit power control operations astaught herein. For example, a transmit power control component 1290 maycooperate with the processor 1230 and/or other components of the device1210 to control transmit power for transmissions by the device 1210(e.g., transmissions to another device such as the device 1250) astaught herein. It should be appreciated that for each device 1210 and1250 the functionality of two or more of the described components may beprovided by a single component. For example, a single processingcomponent may provide the functionality of the transmit power controlcomponent 1290 and the processor 1230.

The teachings herein may be incorporated into various types ofcommunication systems and/or system components. In some aspects, theteachings herein may be employed in a multiple-access system capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., by specifying one or more of bandwidth, transmitpower, coding, interleaving, and so on). For example, the teachingsherein may be applied to any one or combinations of the followingtechnologies: Code Division Multiple Access (CDMA) systems,Multiple-Carrier CDMA (MCCDMA), Wideband CDMA (W-CDMA), High-SpeedPacket Access (HSPA, HSPA+) systems, Time Division Multiple Access(TDMA) systems, Frequency Division Multiple Access (FDMA) systems,Single-Carrier FDMA (SC-FDMA) systems, Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, or other multiple access techniques. Awireless communication system employing the teachings herein may bedesigned to implement one or more standards, such as IS-95, cdma2000,IS-856, W-CDMA, TDSCDMA, and other standards. A CDMA network mayimplement a radio technology such as Universal Terrestrial Radio Access(UTRA), cdma2000, or some other technology. UTRA includes W-CDMA and LowChip Rate (LCR). The cdma2000 technology covers IS-2000, IS-95 andIS-856 standards. A TDMA network may implement a radio technology suchas Global System for Mobile Communications (GSM). An OFDMA network mayimplement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11,IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM arepart of Universal Mobile Telecommunication System (UMTS). The teachingsherein may be implemented in a 3GPP Long Term Evolution (LTE) system, anUltra-Mobile Broadband (UMB) system, and other types of systems. LTE isa release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE aredescribed in documents from an organization named “3rd GenerationPartnership Project” (3GPP), while cdma2000 is described in documentsfrom an organization named “3rd Generation Partnership Project 2”(3GPP2). Although certain aspects of the disclosure may be describedusing 3GPP terminology, it is to be understood that the teachings hereinmay be applied to 3GPP (e.g., Rel99, Rel5, Rel6, Rel7) technology, aswell as 3GPP2 (e.g., 1xRTT, 1xEV-DO Rel0, RevA, RevB) technology andother technologies.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of apparatuses (e.g., nodes). In someaspects, a node (e.g., a wireless node) implemented in accordance withthe teachings herein may comprise an access point or an access terminal.

For example, an access terminal may comprise, be implemented as, orknown as user equipment, a subscriber station, a subscriber unit, amobile station, a mobile, a mobile node, a remote station, a remoteterminal, a user terminal, a user agent, a user device, or some otherterminology. In some implementations an access terminal may comprise acellular telephone, a cordless telephone, a session initiation protocol(SIP) phone, a wireless local loop (WLL) station, a personal digitalassistant (PDA), a handheld device having wireless connectioncapability, or some other suitable processing device connected to awireless modem. Accordingly, one or more aspects taught herein may beincorporated into a phone (e.g., a cellular phone or smart phone), acomputer (e.g., a laptop), a portable communication device, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music device, a video device, or a satellite radio), aglobal positioning system device, or any other suitable device that isconfigured to communicate via a wireless medium.

An access point may comprise, be implemented as, or known as a NodeB, aneNodeB, a radio network controller (RNC), a base station (BS), a radiobase station (RBS), a base station controller (BSC), a base transceiverstation (BTS), a transceiver function (TF), a radio transceiver, a radiorouter, a basic service set (BSS), an extended service set (ESS), amacro cell, a macro node, a Home eNB (HeNB), a femto cell, a femto node,a pico node, or some other similar terminology.

In some aspects a node (e.g., an access point) may comprise an accessnode for a communication system. Such an access node may provide, forexample, connectivity for or to a network (e.g., a wide area networksuch as the Internet or a cellular network) via a wired or wirelesscommunication link to the network. Accordingly, an access node mayenable another node (e.g., an access terminal) to access a network orsome other functionality. In addition, it should be appreciated that oneor both of the nodes may be portable or, in some cases, relativelynon-portable.

Also, it should be appreciated that a wireless node may be capable oftransmitting and/or receiving information in a non-wireless manner(e.g., via a wired connection). Thus, a receiver and a transmitter asdiscussed herein may include appropriate communication interfacecomponents (e.g., electrical or optical interface components) tocommunicate via a non-wireless medium.

A wireless node may communicate via one or more wireless communicationlinks that are based on or otherwise support any suitable wirelesscommunication technology. For example, in some aspects a wireless nodemay associate with a network. In some aspects the network may comprise alocal area network or a wide area network. A wireless device may supportor otherwise use one or more of a variety of wireless communicationtechnologies, protocols, or standards such as those discussed herein(e.g., CDMA, TDMA, OFDM, OFDMA, WiMAX, Wi-Fi, and so on). Similarly, awireless node may support or otherwise use one or more of a variety ofcorresponding modulation or multiplexing schemes. A wireless node maythus include appropriate components (e.g., air interfaces) to establishand communicate via one or more wireless communication links using theabove or other wireless communication technologies. For example, awireless node may comprise a wireless transceiver with associatedtransmitter and receiver components that may include various components(e.g., signal generators and signal processors) that facilitatecommunication over a wireless medium.

The functionality described herein (e.g., with regard to one or more ofthe accompanying figures) may correspond in some aspects to similarlydesignated “means for” functionality in the appended claims. Referringto FIGS. 13-17, apparatuses 1300, 1400, 1500, 1600, and 1700 arerepresented as a series of interrelated functional modules. Here, amodule for transmitting data on a forward link 1302 or 1402 maycorrespond at least in some aspects to, for example, a transmitter asdiscussed herein. A module for transmitting beacons on a beacon channel1304 or 1404 may correspond at least in some aspects to, for example, atransmitter as discussed herein. A module for receiving messages 1306 or1406 may correspond at least in some aspects to, for example, a receiveras discussed herein. A module for controlling transmit power 1308 or1408 may correspond at least in some aspects to, for example, acontroller as discussed herein. A module for receiving registrationmessages 1310 or 1410 may correspond at least in some aspects to, forexample, a receiver as discussed herein. A module for receiving pilotsignals 1312 or 1412 may correspond at least in some aspects to, forexample, a receiver as discussed herein. A module for identifyingchannel quality 1314 or 1414 may correspond at least in some aspects to,for example, a controller as discussed herein. A module for setting atleast one limit for the transmit power 1316 or 1416 may correspond atleast in some aspects to, for example, a controller as discussed herein.A module for determining that another access terminal is activelyreceiving 1318 or 1418 may correspond at least in some aspects to, forexample, a controller as discussed herein. A module for restrictingtransmission 1320 or 1420 may correspond at least in some aspects to,for example, a controller as discussed herein. A module for receivingsignals 1502 may correspond at least in some aspects to, for example, areceiver as discussed herein. A module for identifying channel quality1504 may correspond at least in some aspects to, for example, acontroller as discussed herein. A module for setting transmit power toan initial value 1506 may correspond at least in some aspects to, forexample, a controller as discussed herein. A module for receivingmeasurement reports 1508 may correspond at least in some aspects to, forexample, a receiver as discussed herein. A module for receivingregistration messages 1510 may correspond at least in some aspects to,for example, a receiver as discussed herein. A module for definingtransmit power limits 1512 may correspond at least in some aspects to,for example, a controller as discussed herein. A module for settingtransmit power to a new value 1514 may correspond at least in someaspects to, for example, a controller as discussed herein. A module fordetermining that another access terminal is actively receiving 1516 maycorrespond at least in some aspects to, for example, a controller asdiscussed herein. A module for restricting transmit power 1518 maycorrespond at least in some aspects to, for example, a controller asdiscussed herein. A module for determining a plurality of path losses1520 may correspond at least in some aspects to, for example, acontroller as discussed herein. A module for repeatedly monitoringsignals 1522 may correspond at least in some aspects to, for example, areceiver as discussed herein. A module for determining whether there hasbeen a change in transmit power 1524 may correspond at least in someaspects to, for example, a controller as discussed herein. A module forrecalibrating transmit power 1526 may correspond at least in someaspects to, for example, a controller as discussed herein. A module formaintaining information indicative of a desired coverage range 1602 maycorrespond at least in some aspects to, for example, a controller asdiscussed herein. A module for receiving signals 1604 may correspond atleast in some aspects to, for example, a receiver as discussed herein. Amodule for determining signal strength information 1606 may correspondat least in some aspects to, for example, a controller as discussedherein. A module for setting transmit power limits 1608 may correspondat least in some aspects to, for example, a controller as discussedherein. A module for controlling transmit power 1610 may correspond atleast in some aspects to, for example, a controller as discussed herein.A module for determining that an initialization procedure has commenced1612 may correspond at least in some aspects to, for example, acontroller as discussed herein. A module for triggering the setting oftransmit power limits 1614 may correspond at least in some aspects to,for example, a controller as discussed herein. A module for determiningthat there has been a change in channel quality 1616 may correspond atleast in some aspects to, for example, a controller as discussed herein.A module for adjusting transmit power limits 1618 may correspond atleast in some aspects to, for example, a controller as discussed herein.A module for receiving registration messages 1620 may correspond atleast in some aspects to, for example, a receiver as discussed herein. Amodule for receiving messages 1622 may correspond at least in someaspects to, for example, a receiver as discussed herein. A module fortransmitting data on a forward link 1702 may correspond at least in someaspects to, for example, a transmitter as discussed herein. A module fortransmitting beacons on a beacon channel 1704 may correspond at least insome aspects to, for example, a transmitter as discussed herein. Amodule for receiving registration messages 1706 may correspond at leastin some aspects to, for example, a receiver as discussed herein. Amodule for controlling transmit power 1708 may correspond at least insome aspects to, for example, a controller as discussed herein.

The functionality of the modules of FIGS. 13-17 may be implemented invarious ways consistent with the teachings herein. In some aspects thefunctionality of these modules may be implemented as one or moreelectrical components. In some aspects the functionality of these blocksmay be implemented as a processing system including one or moreprocessor components. In some aspects the functionality of these modulesmay be implemented using, for example, at least a portion of one or moreintegrated circuits (e.g., an ASIC). As discussed herein, an integratedcircuit may include a processor, software, other related components, orsome combination thereof. The functionality of these modules also may beimplemented in some other manner as taught herein. In some aspects oneor more of any dashed blocks in FIGS. 13-17 are optional.

It should be understood that any reference to an element herein using adesignation such as “first,” “second,” and so forth does not generallylimit the quantity or order of those elements. Rather, thesedesignations may be used herein as a convenient method of distinguishingbetween two or more elements or instances of an element. Thus, areference to first and second elements does not mean that only twoelements may be employed there or that the first element must precedethe second element in some manner. Also, unless stated otherwise a setof elements may comprise one or more elements. In addition, terminologyof the form “at least one of: A, B, or C” used in the description or theclaims means “A or B or C or any combination of these elements.”

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that any of the variousillustrative logical blocks, modules, processors, means, circuits, andalgorithm steps described in connection with the aspects disclosedherein may be implemented as electronic hardware (e.g., a digitalimplementation, an analog implementation, or a combination of the two,which may be designed using source coding or some other technique),various forms of program or design code incorporating instructions(which may be referred to herein, for convenience, as “software” or a“software module”), or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implementedwithin or performed by an integrated circuit (IC), an access terminal,or an access point. The IC may comprise a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, electrical components, optical components,mechanical components, or any combination thereof designed to performthe functions described herein, and may execute codes or instructionsthat reside within the IC, outside of the IC, or both. A general purposeprocessor may be a microprocessor, but in the alternative, the processormay be any conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media. It should beappreciated that a computer-readable medium may be implemented in anysuitable computer-program product.

The previous description of the disclosed aspects is provided to enableany person skilled in the art to make or use the present disclosure.Various modifications to these aspects will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other aspects without departing from the scope of thedisclosure. Thus, the present disclosure is not intended to be limitedto the aspects shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. A method of communication, comprising:transmitting data on a forward link, wherein the forward link data istransmitted by an access point on a first carrier frequency;transmitting beacons on a beacon channel, wherein the beacons aretransmitted by the access point on a second carrier frequency; receivingmessages from at least one access terminal at the access point, whereinthe messages are indicative of channel quality on the second carrierfrequency; and controlling transmit power of the access point based onthe received messages, wherein the transmit power is controlled fortransmissions on the first carrier frequency, the second carrierfrequency, or the first carrier frequency and the second carrierfrequency.
 2. The method of claim 1, wherein the controlling of thetransmit power based on the received messages only controls beacontransmit power on the second carrier frequency.
 3. The method of claim1, further comprising receiving additional messages from the at leastone access terminal at the access point, wherein: the additionalmessages are indicative of: channel quality on the first carrierfrequency, at least one path loss between the at least one accessterminal and the access point, or channel quality on the first carrierfrequency and at least one path loss between the at least one accessterminal and the access point; and the controlling of the transmit poweris further based on the received additional messages.
 4. The method ofclaim 1, wherein: the messages are received over a period of time; andthe controlling of the transmit power based on the received messagescomprises adjusting the transmit power upon expiration of the period oftime.
 5. The method of claim 1, further comprising receivingregistration messages at the access point, wherein the controlling ofthe transmit power is further based on the received registrationmessages.
 6. The method of claim 5, wherein: the registration messagesare received over a period of time; and the controlling of the transmitpower based on the received registration messages comprises adjustingthe transmit power upon expiration of the period of time.
 7. The methodof claim 5, wherein the controlling of the transmit power based on thereceived registration messages comprises: classifying an access terminalthat sent at least one of the registration messages as a neighboringalien access terminal or a non-neighboring alien access terminal; andadjusting the transmit power according to different criteria dependingon whether the access terminal is classified as a neighboring alienaccess terminal or a non-neighboring alien access terminal.
 8. Themethod of claim 7, wherein the classification of the access terminal isbased on a period of time that the access terminal has camped on theaccess point.
 9. The method of claim 7, wherein the classification ofthe access terminal is based on a quantity of registration attempts thatthe access terminal has made at the access point over a period of time.10. The method of claim 5, wherein: the controlling of the transmitpower based on the received messages comprises establishing transmitpower limits based on the channel quality on the second carrierfrequency; the received registration messages correspond to a quantityof registration attempts made by at least one other access terminal overa period of time; the at least one other access terminal is notauthorized to receive active mode service via the access point; and thecontrolling of the transmit power based on the received registrationmessages comprising adjusting the transmit power within the transmitpower limits based on the quantity of registration attempts.
 11. Themethod of claim 5, further comprising: receiving pilot signals from atleast one other access point on the second carrier frequency;identifying channel quality at the access point based on the receivedpilot signals; and setting at least one limit for the transmit powerbased on the identified channel quality.
 12. The method of claim 11,further comprising: determining that another access terminal near theaccess point is actively receiving information from one of the at leastone other access point or another access point on the second carrierfrequency; and restricting transmission by the access point on thesecond carrier frequency as a result of the determination.
 13. Themethod of claim 1, wherein: the received messages include informationindicative of channel quality at a plurality of locations; the receivedmessages further include information indicative of path losses betweenthe access point and the plurality of locations; the controlling of thetransmit power comprises setting a minimum transmit power that providescoverage for a subset of the locations; and the setting of the minimumtransmit power is based on: the path losses corresponding to the subsetof locations, the information indicative of the channel quality at thesubset of locations, or the path losses corresponding to the subset oflocations and the information indicative of the channel quality at thesubset of locations.
 14. The method of claim 13, wherein: theinformation indicative of channel quality comprises pilot signalstrengths of pilot signals that the at least one access terminalreceived from at least one other access point; and the informationindicative of path losses comprises pilot signal strengths of pilotsignals that the at least one access terminal received from the accesspoint.
 15. The method of claim 1, wherein the controlling of thetransmit power comprises specifying first transmit power limits fortransmission of low power beacons and specifying second transmit powerlimits for transmission of high power beacons.
 16. The method of claim1, wherein the received messages comprise pilot strength measurementmessages, measurement report messages, or candidate frequency searchreport messages.
 17. The method of claim 1, wherein the at least oneaccess terminal comprises at least one home access terminal for theaccess point or at least one closed subscriber group access terminalassociated with the access point.
 18. An apparatus for communication,comprising: a transmitter operable to transmit data on a forward linkand transmit beacons on a beacon channel, wherein the forward link datais transmitted on a first carrier frequency and the beacons aretransmitted on a second carrier frequency; a receiver operable toreceive messages from at least one access terminal, wherein the messagesare indicative of channel quality on the second carrier frequency; and acontroller operable to control transmit power of the transmitter basedon the received messages, wherein the transmit power is controlled fortransmissions on the first carrier frequency, the second carrierfrequency, or the first carrier frequency and the second carrierfrequency.
 19. The apparatus of claim 18, wherein the controlling of thetransmit power based on the received messages only controls beacontransmit power on the second carrier frequency.
 20. The apparatus ofclaim 18, wherein: the receiver is further operable to receiveadditional messages from the at least one access terminal; theadditional messages are indicative of: channel quality on the firstcarrier frequency, at least one path loss between the at least oneaccess terminal and the apparatus, or channel quality on the firstcarrier frequency and at least one path loss between the at least oneaccess terminal and the apparatus; and the controlling of the transmitpower is further based on the received additional messages.
 21. Theapparatus of claim 18, wherein: the receiver is further operable toreceive registration messages; and the controlling of the transmit poweris further based on the received registration messages.
 22. Theapparatus of claim 21, wherein the controlling of the transmit powerbased on the received registration messages comprises: classifying anaccess terminal that sent at least one of the registration messages as aneighboring alien access terminal or a non-neighboring alien accessterminal; and adjusting the transmit power according to differentcriteria depending on whether the access terminal is classified as aneighboring alien access terminal or a non-neighboring alien accessterminal.
 23. The apparatus of claim 21, wherein: the controlling of thetransmit power based on the received messages comprises establishingtransmit power limits based on the channel quality on the second carrierfrequency; the received registration messages correspond to a quantityof registration attempts made by at least one other access terminal overa period of time; the at least one other access terminal is notauthorized to receive active mode service via the apparatus; and thecontrolling of the transmit power based on the received registrationmessages comprising adjusting the transmit power within the transmitpower limits based on the quantity of registration attempts.
 24. Theapparatus of claim 21, wherein: the receiver is further operable toreceive pilot signals from at least one access point on the secondcarrier frequency; the controller is further operable to identifychannel quality at the apparatus based on the received pilot signals;and the controller is further operable to set at least one limit for thetransmit power based on the identified channel quality.
 25. Theapparatus of claim 24, wherein the controller is further operable to:determine that another access terminal near the apparatus is activelyreceiving information from one of the at least one access point oranother access point on the second carrier frequency; and restricttransmission by the transmitter on the second carrier frequency as aresult of the determination.
 26. The apparatus of claim 18, wherein: thereceived messages include information indicative of channel quality at aplurality of locations; the received messages further includeinformation indicative of path losses between the apparatus and theplurality of locations; the controlling of the transmit power comprisessetting a minimum transmit power that provides coverage for a subset ofthe locations; and the setting of the minimum transmit power is basedon: the path losses corresponding to the subset of locations, theinformation indicative of the channel quality at the subset oflocations, or the path losses corresponding to the subset of locationsand the information indicative of the channel quality at the subset oflocations.
 27. An apparatus for communication, comprising: means fortransmitting data on a forward link and transmitting beacons on a beaconchannel, wherein the forward link data is transmitted on a first carrierfrequency and the beacons are transmitted on a second carrier frequency;means for receiving messages from at least one access terminal, whereinthe messages are indicative of channel quality on the second carrierfrequency; and means for controlling transmit power of the means fortransmitting based on the received messages, wherein the transmit poweris controlled for transmissions on the first carrier frequency, thesecond carrier frequency, or the first carrier frequency and the secondcarrier frequency.
 28. The apparatus of claim 27, wherein thecontrolling of the transmit power based on the received messages onlycontrols beacon transmit power on the second carrier frequency.
 29. Theapparatus of claim 27, further comprising means for receiving additionalmessages from the at least one access terminal, wherein: the additionalmessages are indicative of: channel quality on the first carrierfrequency, at least one path loss between the at least one accessterminal and the apparatus, or channel quality on the first carrierfrequency and at least one path loss between the at least one accessterminal and the apparatus; and the controlling of the transmit power isfurther based on the received additional messages.
 30. The apparatus ofclaim 27, further comprising means for receiving registration messages,wherein the controlling of the transmit power is further based on thereceived registration messages.
 31. The apparatus of claim 30, whereinthe controlling of the transmit power based on the received registrationmessages comprises: classifying an access terminal that sent at leastone of the registration messages as a neighboring alien access terminalor a non-neighboring alien access terminal; and adjusting the transmitpower according to different criteria depending on whether the accessterminal is classified as a neighboring alien access terminal or anon-neighboring alien access terminal.
 32. The apparatus of claim 30,wherein: the controlling of the transmit power based on the receivedmessages comprises establishing transmit power limits based on thechannel quality on the second carrier frequency; the receivedregistration messages correspond to a quantity of registration attemptsmade by at least one other access terminal over a period of time; the atleast one other access terminal is not authorized to receive active modeservice via the apparatus; and the controlling of the transmit powerbased on the received registration messages comprising adjusting thetransmit power within the transmit power limits based on the quantity ofregistration attempts.
 33. The apparatus of claim 30, furthercomprising: means for receiving pilot signals from at least one accesspoint on the second carrier frequency; means for identifying channelquality at the apparatus based on the received pilot signals; and meansfor setting at least one limit for the transmit power based on theidentified channel quality.
 34. The apparatus of claim 33, furthercomprising: means for determining that another access terminal near theapparatus is actively receiving information from one of the at least oneaccess point or another access point on the second carrier frequency;and means for restricting transmission by the means for transmitting onthe second carrier frequency as a result of the determination.
 35. Theapparatus of claim 27, wherein: the received messages includeinformation indicative of channel quality at a plurality of locations;the received messages further include information indicative of pathlosses between the apparatus and the plurality of locations; thecontrolling of the transmit power comprises setting a minimum transmitpower that provides coverage for a subset of the locations; and thesetting of the minimum transmit power is based on: the path lossescorresponding to the subset of locations, the information indicative ofthe channel quality at the subset of locations, or the path lossescorresponding to the subset of locations and the information indicativeof the channel quality at the subset of locations.
 36. Acomputer-program product, comprising: computer-readable mediumcomprising code for causing a computer to: transmit data on a forwardlink, wherein the forward link data is transmitted by an access point ona first carrier frequency; transmit beacons on a beacon channel, whereinthe beacons are transmitted by the access point on a second carrierfrequency; receive messages from at least one access terminal at theaccess point, wherein the messages are indicative of channel quality onthe second carrier frequency; and control transmit power of the accesspoint based on the received messages, wherein the transmit power iscontrolled for transmissions on the first carrier frequency, the secondcarrier frequency, or the first carrier frequency and the second carrierfrequency.
 37. The computer-program product of claim 36, wherein thecontrolling of the transmit power based on the received messages onlycontrols beacon transmit power on the second carrier frequency.
 38. Thecomputer-program product of claim 36, wherein: the computer-readablemedium further comprises code for causing the computer to receiveadditional messages from the at least one access terminal at the accesspoint; the additional messages are indicative of: channel quality on thefirst carrier frequency, at least one path loss between the at least oneaccess terminal and the access point, or channel quality on the firstcarrier frequency and at least one path loss between the at least oneaccess terminal and the access point; and the controlling of thetransmit power is further based on the received additional messages. 39.The computer-program product of claim 36, wherein: the computer-readablemedium further comprises code for causing the computer to receiveregistration messages at the access point; and the controlling of thetransmit power is further based on the received registration messages.40. The computer-program product of claim 39, wherein the controlling ofthe transmit power based on the received registration messagescomprises: classifying an access terminal that sent at least one of theregistration messages as a neighboring alien access terminal or anon-neighboring alien access terminal; and adjusting the transmit poweraccording to different criteria depending on whether the access terminalis classified as a neighboring alien access terminal or anon-neighboring alien access terminal.
 41. The computer-program productof claim 39, wherein: the controlling of the transmit power based on thereceived messages comprises establishing transmit power limits based onthe channel quality on the second carrier frequency; the receivedregistration messages correspond to a quantity of registration attemptsmade by at least one other access terminal over a period of time; the atleast one other access terminal is not authorized to receive active modeservice via the access point; and the controlling of the transmit powerbased on the received registration messages comprising adjusting thetransmit power within the transmit power limits based on the quantity ofregistration attempts.
 42. The computer-program product of claim 39,wherein the computer-readable medium further comprises code for causingthe computer to: receive pilot signals from at least one other accesspoint on the second carrier frequency; identify channel quality at theaccess point based on the received pilot signals; and set at least onelimit for the transmit power based on the identified channel quality.43. The computer-program product of claim 42, wherein thecomputer-readable medium further comprises code for causing the computerto: determine that another access terminal near the access point isactively receiving information from one of the at least one other accesspoint or another access point on the second carrier frequency; andrestrict transmission by the access point on the second carrierfrequency as a result of the determination.
 44. The computer-programproduct of claim 36, wherein: the received messages include informationindicative of channel quality at a plurality of locations; the receivedmessages further include information indicative of path losses betweenthe access point and the plurality of locations; the controlling of thetransmit power comprises setting a minimum transmit power that providescoverage for a subset of the locations; and the setting of the minimumtransmit power is based on: the path losses corresponding to the subsetof locations, the information indicative of the channel quality at thesubset of locations, or the path losses corresponding to the subset oflocations and the information indicative of the channel quality at thesubset of locations.
 45. A method of communication, comprising:transmitting data on a forward link of an access point, wherein theforward link data is transmitted by the access point on a first carrierfrequency; transmitting beacons on a beacon channel, wherein the beaconsare transmitted by the access point on a second carrier frequency;receiving messages from at least one access terminal at the accesspoint, wherein the messages are indicative of: channel quality on thefirst carrier frequency, at least one path loss between the at least oneaccess terminal and the access point, or channel quality on the firstcarrier frequency and at least one path loss between the at least oneaccess terminal and the access point; and controlling transmit power ofthe access point based on the received messages, wherein the transmitpower is controlled for transmissions on the second carrier frequency.46. The method of claim 45, wherein the controlling of the transmitpower based on the received messages further controls transmit power fortransmissions on the first carrier frequency.
 47. The method of claim45, further comprising receiving registration messages at the accesspoint, wherein the controlling of the transmit power is further based onthe received registration messages.
 48. The method of claim 47, wherein:the controlling of the transmit power based on the received messagescomprises establishing transmit power limits based on the channelquality on the first carrier frequency; the received registrationmessages correspond to a quantity of registration attempts made by atleast one other access terminal over a period of time; the at least oneother access terminal is not authorized to receive active mode servicevia the access point; and the controlling of the transmit power based onthe received registration messages comprising adjusting the transmitpower within the transmit power limits based on the quantity ofregistration attempts.
 49. The method of claim 48, further comprising:receiving pilot signals from at least one other access point on thesecond carrier frequency; identifying channel quality at the accesspoint based on the received pilot signals; and setting at least onelimit for the transmit power based on the identified channel quality.50. The method of claim 49, further comprising: determining that anotheraccess terminal near the access point is actively receiving informationfrom one of the at least one other access point or another access pointon the second carrier frequency; and restricting transmission by theaccess point on the second carrier frequency as a result of thedetermination.
 51. An apparatus for communication, comprising: atransmitter operable to transmit data on a forward link and transmitbeacons on a beacon channel, wherein the forward link data istransmitted on a first carrier frequency and the beacons are transmittedon a second carrier frequency; a receiver operable to receive messagesfrom at least one access terminal, wherein the messages are indicativeof: channel quality on the first carrier frequency, at least one pathloss between the at least one access terminal and the apparatus, orchannel quality on the first carrier frequency and at least one pathloss between the at least one access terminal and the apparatus; and acontroller operable to control transmit power of the transmitter basedon the received messages, wherein the transmit power is controlled fortransmissions on the second carrier frequency.
 52. The apparatus ofclaim 51, wherein the controlling of the transmit power based on thereceived messages further controls transmit power for transmissions onthe first carrier frequency.
 53. The apparatus of claim 51, wherein: thereceiver is further operable to receive registration messages; and thecontrolling of the transmit power is further based on the receivedregistration messages.
 54. The apparatus of claim 53, wherein: thecontrolling of the transmit power based on the received messagescomprises establishing transmit power limits based on the channelquality on the first carrier frequency; the received registrationmessages correspond to a quantity of registration attempts made by atleast one other access terminal over a period of time; the at least oneother access terminal is not authorized to receive active mode servicevia the apparatus; and the controlling of the transmit power based onthe received registration messages comprising adjusting the transmitpower within the transmit power limits based on the quantity ofregistration attempts.
 55. An apparatus for communication, comprising:means for transmitting data on a forward link and transmitting beaconson a beacon channel, wherein the forward link data is transmitted on afirst carrier frequency and the beacons are transmitted by the accesspoint on a second carrier frequency; means for receiving messages fromat least one access terminal, wherein the messages are indicative of:channel quality on the first carrier frequency, at least one path lossbetween the at least one access terminal and the apparatus, or channelquality on the first carrier frequency and at least one path lossbetween the at least one access terminal and the apparatus; and meansfor controlling transmit power of the means for transmitting based onthe received messages, wherein the transmit power is controlled fortransmissions on the second carrier frequency.
 56. The apparatus ofclaim 55, wherein the controlling of the transmit power based on thereceived messages further controls transmit power for transmissions onthe first carrier frequency.
 57. The apparatus of claim 55, furthercomprising means for receiving registration messages, wherein thecontrolling of the transmit power is further based on the receivedregistration messages.
 58. The apparatus of claim 57, wherein: thecontrolling of the transmit power based on the received messagescomprises establishing transmit power limits based on the channelquality on the first carrier frequency; the received registrationmessages correspond to a quantity of registration attempts made by atleast one other access terminal over a period of time; the at least oneother access terminal is not authorized to receive active mode servicevia the apparatus; and the controlling of the transmit power based onthe received registration messages comprising adjusting the transmitpower within the transmit power limits based on the quantity ofregistration attempts.
 59. A computer-program product, comprising:computer-readable medium comprising code for causing a computer to:transmit data on a forward link of an access point, wherein the forwardlink data is transmitted by the access point on a first carrierfrequency; transmit beacons on a beacon channel, wherein the beacons aretransmitted by the access point on a second carrier frequency; receivemessages from at least one access terminal at the access point, whereinthe messages are indicative of: channel quality on the first carrierfrequency, at least one path loss between the at least one accessterminal and the access point, or channel quality on the first carrierfrequency and at least one path loss between the at least one accessterminal and the access point; and control transmit power of the accesspoint based on the received messages, wherein the transmit power iscontrolled for transmissions on the second carrier frequency.
 60. Thecomputer-program product of claim 59, wherein the controlling of thetransmit power based on the received messages further controls transmitpower for transmissions on the first carrier frequency.
 61. Thecomputer-program product of claim 59, wherein: the computer-readablemedium further comprises code for causing the computer to receiveregistration messages at the access point; and the controlling of thetransmit power is further based on the received registration messages.62. The computer-program product of claim 61, wherein: the controllingof the transmit power based on the received messages comprisesestablishing transmit power limits based on the channel quality on thefirst carrier frequency; the received registration messages correspondto a quantity of registration attempts made by at least one other accessterminal over a period of time; the at least one other access terminalis not authorized to receive active mode service via the access point;and the controlling of the transmit power based on the receivedregistration messages comprising adjusting the transmit power within thetransmit power limits based on the quantity of registration attempts.